I would not call an RX-8 underpowered by any means. You really need to know how to use the engine to get the power out of the car, shifting high and keeping the revs always up because that is where all the hp/ torque lies. Ill have you guys know, yesterday Me in the ML55, and Friends in RX8 (stock) Modded 03 WRX 230hp to wheel dyno tuned., exhaust cutout intercooler spray full exhaust, and a few other little goodies.), and lightly modded Mx-5. The Rx-8 kept pace for pace with a AWD Modded WRX without problems. (While I took them all out in the ML after 120mph haha) But anyway, the Rx-8 is an amazingly good car, mod it and the car really will be hard to touch by anything.

As for the A4, extremely good potential on all fronts, but you pay the costs of reliabilty. I havent had my god damn car for 2 weeks now =/

 

350 Z if you plan on twin turbo

RX-8 if you plan on the new Supercharger coming out for the Rotary.