G37 would be good or a GTO 6 speed b/c the auto that GM puts in it well its not very good. Also for that money you can pick up a C5 vette Z06 or a WS6 or Camaro SS and mod them out. I know you can easly and for cheap make 420hp out of an LS1 with just header, exhust, intake, chip, and intake manifold. Then you can get new heads from GM proformance off the LS6 or 7 and and a cam and hit +500