personally i would go with a GSX 750 motor. Suzi make the best motorcycle motors for power IMO. I have had Honda (eh okay) Yamaha's (better) and Kawasaki's (pretty sout), but suzi's have always felt the most powerful per cc.
You guys gotta ride the new TRX450R. Makes the raptor feel like a pick up. Its light and fast as hell. My friend ran 16.1 in the quarter on his. Beat my friends auto civic by 3 seconds hahahah
dude.... a stock raptor runs 15.5........ sorry to burst your bubble that thats a half second on your trx450r.....
thanks guys ill keep you all posted... yes a extended arm is something i am thinking about as is how im going to mount my turbo next winter onto this thing.. i want to hide it in the factory airbox sneeky sneeky
i made one outta steel this year that mimics the factory piece.. so im only worried about how hot it will get on my bottom... LOL but i think i have coold it by cutting a couple holes into the box to allow the ram air affect and hopefully cool it down.