i still wouldnt get a 335/135..those cars are everywhere and i only see 400-450whp as their max...reliability is a concern..and even if you have that much power, they would probably still get smoked by a bolt on Z on a track with turns..considering the fact that a 3 liter twin turbo is making 300 hp is not impressive at all...there are better motors out there...LSX, VQ/VR, the S4's new motor, even the Evo's alum block is impressive...a VQ with twin turbo, although quite expensive is way above the level of the 135s/335s limits...
edit
ops he already picked his car..well in that case..enjoy it to your fullest...