Check out the Institute of Human Performance site here - and read below for a reminder that a LIL' rest can make a BIG difference.
Good rest time
(49-56 hours per week).
Enough can’t be said about getting good rest. If you have to sacrifice time for work or family, rest time is usually the first to go. If you make that mistake, you will surely suffer. However, the price you pay when you give up your rest is difficult to detect because it happens so slowly and over such a long time. Most Americans are sleep deprived even though they spend many hours in bed or watching TV, playing video games, surfing the Internet, and so on. If your mind is flying, you are not resting. Imagery (i.e., perception) is everything; if you are sitting down and imagining you are running, you are not resting—you are running. Go to bed early and take naps even if you can do so only on the weekends. View naps and good rest time as a miniature vacation from the chaos we all call life.