well, At one point I was under the impression that boosted Renesis' weren't as powerfull but Mazdamaniac and others showed me otherwise.
http://www.mazdamaniac.com/cobb/accessport.htm
He's making ~350hp which is pretty nice for the RX8 chassis.
If you have money to throw around then go for a 3-rotor.....power, more torque and it's perfect for the rx8.