NOCO,
Get a Crystalyte 5300 series hub motor. they are rated at 750W, but have been shown to handle in excess of 5KW. They are a bit expensive but worth the money. You'll want a 72v controller for the system. I have the weakest controller made for that voltage and I can still run 30mph if I need to. there are people running them above 50 mph.
Check this link
http://endless-sphere.com/forums/viewforum.php?f=2
Should give a good overview of some of the things going on in the homebrew ebike world.
JJ