I once played a D&D game with a buddy of mine where he completely overhauled the rules to make it more realistic. This was back in Jan 2003. In his system you had three different pools of HP per se. The first one was considered ''fluff.''
Your fluff HP was the bruising and superficial...
Its been almost a year so I don't know if this forum has moved on but I have a few suggestions. I agree with the idea that AC should get lower as your stamina / fatigue levels go down. I also agree with the idea of how fighter / barbarian and wizard / sorcerer should be more of a play-style...