I built a Haynes with a 2006 R1 motor... performance is spectacular! It is one of the fastest 7's on our local track, and easily thrashes cars with motors costing 3 times as much.
What lets it down is the constant high revs on the road... 6500 at 60mph with a 3.54 diff. If you want a track day car, with very little cruising.. go for the bike engine. If you want a tourer.. stick to the car engine.
My build diary:
http://www.lotus7.co.nz/forum/viewto...t=72&start=140
I am about to re-power it with a 3sgte ( turbo) motor and 6 speed altezza box... should give me the track performance and the touring comfort.