I'm with everyone here . . . go for the HP. I'm running a 427w, 550 hp and 560 tq and althought I'm only in the go-karting stage, I can tell you that the power is auxilarating!!! A littel daunting at first, but you'll get used to it. As far as streetability, I think it's fine.
I'm running 3.55 rear gears and the TKO with the .82 5th. Most prefer the .82 5th gear ratio over the .64.
Here's a good gearing calculator:
http://http://www.5speedtransmission...alculator.html
Good luck and have fun!
Matt