cobb stage 2 is great....the car is alot funner to drive and is alot quicker. You don't need to get cobbs turboback..its super expensive. There are plenty of options on what turboback to get, read unabombers posts...theres alotta info there.
supposedly cobb stage 2 can keep up with a stock sti for a lil while..
if you want a quiet car you can think about getting the turboxs stealthback. Its basically a tbe that allows you to use watever axelback you want. You can just keep your stock muffler with exhaust and and uppipe. That'll put you at stage 2....you'll be fast but quiet. very sleeperish. I had the stealthback w/ stock muffler for awhile..i liked it alot but eventually got a prodrive oval tip exhaust. Car is quite a bit louder but more responsive on the throttle.