Originally Posted by REX8
No, that STI was a purpose built car, with a full undertray, larer trubo (making much more than 320), suspension, etc. It's been covered a thousand times.
Car and Driver Lighting Lap:
E90 M3: 3:05
2011 USDM STI: 3:13.8
That's a killing...not even in the same ballpark. The STi is gonna need a good bit work to keep up on an average road course. You have to think, stock for stock, the STI is even a hair slower than the older M3 on a road course (although their overall performance is similar, in general). Add 80 HP for the E90/92, and yeah...it's a walk. A simple stage II upgrade is not going to get it done on the top end. Especially considering the STIs aero, and loss of power via AWD.
Anyway, to the OP:
The STI is relatively cheap/easy to mod. You can certainly throw money at it to keep up with a stock M3 LR edition. The question is, why are you doing this in the first place? And how much are you going to like the STI when you're done? You're young, so you'll probably be fine with the harsh ride, turbo lag, and econobox interior.
But here's a thought...
Buy a BMW with an N54 (135 or 335). They're getting cheap now...and you'll have the ability to add power on par with his M3 MUCH more cheaply. Plus, you will have the other niceties that go with the car.
I think you are severely overestimating how good the m3 is compared to the sti. Insideline ran a 2012 m3 in the 1/4 mile at a 12.8 @ 111.2. They found a 0.90g skid pad, which the sti beats stock. If you look at the stage 2 sti registry on these forums a lot have hit 111 trap speeds at stage 2.
Also in regards to your previous post the newer WRXs have equal WHP to the sti. His car would indeed likely trap faster than an m3. Hell most stage 2 trap 111, then you add an intercooler and ebcs?