Earlier quoted context omitted.
I've actually experimented a fair amount with my sleeping patterns. For the most part, I find that when I wake up in the morning, I feel tired no matter what (up until around ~10 hours of sleep). What I've also found, however, is that this tiredness usually doesn't translate to how I feel for the rest of the day — I feel good all day no matter whether I get 6 or 8 hours.
I felt the same way until I was diagnosed with sleep apnea, even though I don't have any of the usual symptoms such as snoring, obesity, etc.
I still haven't started using a CPAP machine, as I have developed other coping methods (sleeping on one side helps dramatically). I have considered doing another sleep study though, to get some more information and start with a CPAP machine for backup.