how big is too big? probably anything over 5", but i think it's the loudness that really matters. i've heard some loud subarus and i don't like it. most people who put on an exhaust made for a subaru will get nice results. i think the picture of the RS that was posted looks good. that looks like a greddy exhaust. after a certain size you just look dumb, i think. you have to use common sense, if you can.