Ah, there's the kind of PEACHing I like, point-by-point. I shall respond in kind (I skip anything you say is fine).

HD and BAB: I'll concede the point on the die and switch to D12; my thought was to give him more HP, as this pretty much is his counter to most of what a caster throws at him, along with Mettle. So I'll probably drop it to D12 and throw the Evasion abilities in there somewhere (which reminds me, I created an Improved Mettle that I forgot to add in...). As for BAB, I like the two-per-level, and for a reason: I originally had it as a bonus to attack equal to his class level, but this gave him an attack of 40/35/30/25, which struck me as a little too good, so I went with double BAB to give him 40/30/20/10. Still really good, but now at least one of his attacks is semi-average.

Mighty Blows: I think you're right, I'll drop it to a damage bonus equal to 1 per Mighty Warrior class level. This cuts his critical damage pretty near in half, so it's a big cut, but it makes him way less overkill.

Unstoppable Blows/Killing Blows: Is this a little more balanced after cutting the flat damage bonus he gets? I'd like opinions on this before I change it. I want him to be getting a crit at least once a round, and doing at least 5x on it. Also, I'm unfamiliar with the weapon referenced, where is it from?

Channeled Rage: I like this, personally, but you say too much? Maybe half his class level in points?

Two Handed Savagery: Not sure how you're getting your numbers here. Assuming a base Str of 16, he gets his Str mod of +3 multiplied by 12, or +36 damage to his attack at 20th level, not overpowered at all. How did you get +180?

Slay: I honestly don't see a problem with this ability, nor a way to make it not as broken as everyone seems to think it is. Suggestions?

Damage Preference: Let me start with this: if you remove someone's limbs and your DM doesn't RP in side effects, he's a terrible DM. Yes, I know RAW it doesn't give penalties; at any table I've played at, though, you lose an arm and there's side effects. So these effects are less "here's a hard number of "oh crap" to slap on at limb loss" and more "GMs, this is a heads up for how you handle limb loss" (because every GM handles it differently, pretty much). For bludgeoning, yes it's powerful; is it too powerful? Not sure, I'd have to playtest it, but I really don't think it is. He can only really apply his side effects to one character a round, and when he actually gets the truly powerful ability at level 20, he's, um, 20th level. As for piercing, should I increase the Dex penalty? I thought 1 Dex damage a hit was severe enough, but I could make it 2 easily enough, or 1 Con damage.

Savage Frenzy: You didn't say if it was a good thing or a bad thing. I thought doing massive damage to one creature for -15 to AC for the round was a good balance. Is it?

Surge of Rage: Underpowered? There's something I didn't expect. Suggestions for improvement?

Spirit Crushing Rage: This is a move action that effects just the one foe he's focusing on. Can't believe I forgot that, thanks for pointing it out. What did you think of the terrified status, if I may ask? Took me a bit to come up with it.

Perfected Rage: Is taking away the damage rolling a problem? You don't specify.

Thanks for working some of those numbers for me, they help. How does it look after implementing the changes here?