Honestly if I wanted that much power, I'd look at a Evo 9. With minimal mods and I mean minimal, those cars can put down some nice numbers. And if somebody can afford to build a 400whp, then they can definitely afford a used Evo. Evo 8's, depending on miles go for relatively cheap. I'd be weary of the 5 speed on the 02-03 years of the WRX. But, the 2.0 WRX can put out the power, just need the money to do it.