Steve, why not just get a moped?
High power (over 350W) electric bikes really aren't that good. There are some good 350W motors, which when combined with a decent battery which is the most expensive part produce great results even for large/heavy riders.
If you're not already reading it, the Endless Sphere forum has a lot of good info: http://endless-sphere.com/forums/
Electric bikes
Moderator: Peak Moderation