It's almost my birthday, so I have exhaust ??'s
 

Ok, so my cat is making awful noises so I spread the propaganda and my parents are probably going to replace some of my exhast for my birthday coming up. I figured I'll get it all done at once and pay up the balance so I'm getting hoshot headers, a high flow cat, a high flow muffler and piping.

The question is, I plan on keeping this car NA, with engine work like pistons and such further down the line. What is the optimal size for the exhaust piping if I don't plan on boosting. I heard 3" if boosting, 2.5" if not, does this sound right? Or should I go 2.25"? I'm looking to keep good low and mid end pull but definitely want an increase up top. Any advice?

Also, while I'm asking, should I just get a universal muffler like a Flowmaster or something? I want power, but I can't be putting up with a loud drone at highway speeds, I like my stereo too much to make it compete. Loud growl at open throttle is cool, but if it's annoying at like 3k rpms then it won't do. Any suggestions here? Thanks guys.