Thanks for your reply and providing some more insight. From the research I've done, it would seem the reason we do best on 6-8 hours is because that is how long it takes for us to complete 3-4 cycles of stage 4-5 sleep, which are the only ones the body really uses to regenerate, commit information to memory, etc.

My own experiment with Polyphasic sleep seemed conclusive to this however only lasted about 2-3 weeks, as I found it near impossible to maintain while having an active and social life due to its strict requirements.