Since Talisman mentioned balance vs. monster CRs more than once, I figure running a Same Game Challenge's only fair.
ECL 5
Hellste Speer
NG Human Bright Blade 5
Str 14 Dex 10 Con 12 Int 13 Wis 08 Cha 17
Bluff +10
Concentration +9
Diplomacy +10
Sense Motive +7
Spellcraft +9
Improved Initiative
Combat Expertise
Combat Reflexes
Power Attack
3x2
Swift walker
Wildstrike 5/day
Unearthly grace
Lucky dodge
Uncanny dodge
Flashing blade
HP 31
AC 18/0/6
Fort +6
Refl +8
Will +7
Init +4
Melee +8, 1d8+4 (x3) - longspear
Ranged +6, 1d8+2 (x3) - longbow
Wildstrike +1d6+3/1d10
Grapple +7
+1 longspear (2)
+1 breastplate (1)
Masterwork longbow
Shortsword
Sap
Flour sack
Cloak of charisma +2 (4)
Cloak of resistance +1 (1)
---
A huge Animated iron statue: expeditious retreat (wall walker for extra cheese if need be), wildstrike on longbow; don't ask. Sure win.
A Basilisk: despite the sure ambush, I'll hardly get stoned, and I'll kill it faster in melee (which it can't avoid either). Probable win.
A Large Fire Elemental: might get ambushed; otherwise, expeditious retreat + cold longbow. Even match.
A Manticore on the wing: two-shotted. Sure loss.
A Mummy: will get ambushed. Even if paralyzed, remove fear (mental action only ...) + fire longbow. Sure win.
A Phase Spider: after being first attacked, readying full-PA attacks should kill it before the poison returns the favor. But even with defensive precognition up, I have a fair chance of dying 1 min after. Even match.
A Troll: if not grappled to death in the first/surprise round, just let the fire damage from the longbow build. Probable win.
A chasm: wall walker (it seems we're talking dungeon here). Sure win.
A moat filled with acid: assuming it's concealed, sure loss.
A locked door behind a number of pit traps: wall walker after likely falling the first time, bashing the door open shouldn't be a problem. Sure win.
A couple of Centaur Archers in the woods: each can be one-shotted, but this will start with a very painful ambush. Probable loss.
A Howler/Allip tag team: ambush, Will save or die, Wis damage. Sure loss.
A pit filled with medium monstrous scorpions (4): killing them's trivial, I might just die after that, but it's extremely unlikely. Sure win.
A Grimlock assault team (4): assuming I had a torch, Expertised stabbing. Probable win.
A Cleric of Hextor (with his zombies): at least at this point in the game, I'm a better ranged attacker, and should have enough means to keep distance. Probable win.
Sure wins: 5.
Probable wins: 4.
Even matches: 2.
Probable losses: 1.
Sure losses: 3.
Yeah, looks overpowered. It's in the upper range of classes at least.
ECL 10
Hellste Speer
NG Human Bright Blade 10
Str 14 Dex 14 Con 12 Int 13 Wis 08 Cha 21
Bluff +18
Concentration +14
Diplomacy +18
Sense Motive +12
Spellcraft +14
Improved Initiative
Combat Expertise
Combat Reflexes
Power Attack
Point Blank Shot
Rapid Shot
Blind-Fight
4x4
Swift walker
Wildstrike 6/day
Unearthly grace
Lucky dodge
Flashing blade
Smite magic
Woodland stride
Rainbow burst DC 20
Improved uncanny dodge
Flickerstep 50 ft.
Evasion
HP 58
AC 23/2/6
Fort +11
Refl +16
Will +13
Init +6
Melee +13/8, 1d8+4 (x3) - longspear
Ranged +11/11/6, 1d8+3 (x3) - longbow
Wildstrike +2d6+5/1d10
Grapple +12
Ghost touch +1 longspear (8)
+1 breastplate (1)
+1 longbow (2)
Shortsword
Sap
Flour sack
Cloak of charisma +4 (16)
Gloves of dexterity +4 (16)
Cloak of resistance +2 (4)
---
A hallway filled with magical runes: fairly good saves, flight, death ward and a lesser globe of invulnerability should be enough. Probable win.
A Fire Giant: assuming it wastes surprise with a rock instead of closing, flight, fire resistance, temporary hp, cold damage and possibly 4 attacks/round (haste) vs. 1 should carry me through. Probable win.
A Young Blue Dragon: flies faster, burrows (which gives it an ambush) and isn't crunchy like me. Sure loss.
A Bebilith: its ambush will be really painful, but I can slip out of grappling and webs. Still, its poison's awesome - if hit, kiting ceases to be my only option ... probable loss.
A Vrock: ambushed, and possibly stunned. But after that, taking distance and charging does about half the job, and might daze it. Even match.
A tag team of Mind Flayers: nothing they do's likely to work, and they're squishy. Of course, if a mind blast works, that's all. Probable win.
A pair of Remorhazes: the fact that I can avoid its swallowing easily would matter if getting chomped and heated (possibly twice) wasn't enough to kill me. Sure loss.
6 Trolls: kiting should be automatic. Sure win.
A horde of Shadows (12): kiting actually works (however slowly), since I fly faster (despite the sure ambush). Sure win.
Sure wins: 2.
Probable wins: 3.
Even matches: 1.
Probable losses: 1.
Sure losses: 2.
Might be considered OK, especially given that I may be understimating some of them.
ECL 15
Hellste Speer
NG Human Bright Blade 15
Str 20 Dex 16 Con 18 Int 13 Wis 08 Cha 26
Bluff +26
Concentration +22
Diplomacy +26
Sense Motive +17
Spellcraft +19
Improved Initiative
Combat Expertise
Combat Reflexes
Power Attack
Point Blank Shot
Rapid Shot
Blind-Fight
Ability focus (rainbow strike)
Iron Will
5x5
Swift walker
Wildstrike 8/day
Unearthly grace
Lucky dodge
Flashing blade
Woodland stride
Rainbow burst DC 25
Improved uncanny dodge
Evasion
Greater smite magic
Slippery mind
Rainbow blast 9d6, DC 25
Improved flickerstep 75 ft.
HP 131
AC 28/3/8
Fort +22
Refl +25
Will +23
Init +7
Melee +19/14/9, 1d8+8 (x3) - longspear
Ranged +17/17/12/7, 1d8+6 (x3) - longbow
Wildstrike +2d6+8/2d10
Grapple +20
Ghost touch +1 longspear (8)
Ghost touch +1 breastplate (4)
Ghost touch +1 longbow (8)
Shortsword
Sap
Flour sack
Cloak of charisma +6 (36)
Gloves of giant strength +6 (36)
Gloves of dexterity +6 (36)
Periapt of health +6 (36)
Cloak of resistance +5 (25)
Amulet of natural armor +2 (8)
---
A Marut: its DCs need not apply, neither do its own saves vs. dazing. Sure win.
A Hullathoin (with its army of skeletons and bloodfiend locusts): auto-win above ground; under, the army still doesn't count, and the hullathoin itself can't either do much or withstand much. Sure win.
A Nightmare Beast deep in a hedge maze: I fly faster, its DCs don't mean anything. Sure win.
A Windghost in the sky: yay for kiting a flyer! Even if it uses antimagic field, it should still be doable with arrows. It has a good chance of dispelling flight, but at this point I can pretty much fly again (if that was even needed in the first place). Probable win.
A Yakfolk cleric with a party of Dao: really hard to judge due to not knowing their numbers and the wishes. I'll call it a probable loss, because we're talking wish here.
A Drow Priestess with an army of ghouls (30): I'll assume a necromantic build (so she doesn't double as cleric archer so easily). In an open space, flying to her should be easy enough; otherwise, blasting through the ghouls should be easy, the only challenge's not to fail saving throws. Probable win.
A warparty of Cloud Giants (4): flight. Sure win.
A Mature Adult White Dragon: it should get an ambush, kiting's outta question, and it should outdamage me. Probable loss.
A Death Slaad riding a Titanic Toad: even in case of ambush, the slaad can't do much, much less the toad. Sure win.
A Cornugon: hardier, flies, good stun DC: probable loss.
A Gelugon and his Iron Golem bodyguard: given that the gelugon's DCs won't go far, go kiting. Probable win.
A Rube Goldberg series of contingent weirds triggered to a set of symbols of pain surrounding the artifact: sure loss.
A pair of Glabrezus: land-bound + low DCs = sure win, ambush and all.
A harem of Succubi (16): assuming some proximity between them, it's just a matter of blasting; the vrocks might cause some trouble. Probable win.
Twenty Dire Bears: flight. Sure win.
A dozen Medusa mounted archers on Hellcats: flight. Sure win.
A forest made out of lava and infested with hostile fire-element dire badgers: flight. Sure win.
A pair of Beholders: kiting them might be entirely possible, and their DCs are really low. Probable win.
Sure wins: 9.
Probable wins: 5.
Even matches: 0.
Probable losses: 3.
Sure losses: 1.
Ouch. But I maintain that just flight (which PC-classed people in general can counter) did a lot of this.