If you're looking at Stealth bikes, I guess you've seen these.

Bomber Review http://www.electricbike.com/stealth-bomber-review/

Fighter Review http://www.electricbike.com/stealth-fighter/

Hot Rodding by changing the motors, controllers and batteries.
http://www.electricbike.com/stealth-hot-rod/
The Fighter mod is particularly interesting. He's using a tiny 6fet controller and putting 2000w into a Bafang BPM motor with no problems. The author, Kepler, is well known on Endless Sphere for his work on friction motors.