STi like I said you can flash it to get more power. Their ECU's are pretty weird though with their fuzzy logic learning crap. However if you're a man that likes to gamble (which I'm assuming since you're asking about modding a new car
), they're super easy to mod obviously. You just get a cobb tuning flash tool (or borrow one) and flash your ECU and get about 350HP with a new turbo exhaust. These kits (including exhaust) can be had for about 1600 dollars from here...
http://cobbtuning.com/sti/power-s.html#Stage2
Like I said though... the dealership will be able to tell you flashed it. I think the STi and Evo are about the same quartermile wise. The STi gets the DCCD obviously too, you would need the MR (I believe) to get this option. I'm a gadget whore... what can I say.