I'm curently running a comptech header/DC Sports exhaust with 6lbs on a JRSC. Do you think I would make any gains moving up to a 3" Thermal research exhaust and cat? I may be going up to 8lbs soon. I figured it wouldn't hurt.

DC sports exhaust is what -like 2.2" diameter ? Ofcourse go with the 3". The gains are proven. I've seen dynos that show 40+whp gains from switching from a generic ~2" cat-back exhaust to a 3".

Definatly a 3" exhaust would be the best route especialy if your going to up the boost. All aids in helping that engine breath.

Would I be slighting myself keeping the comptech header?

3" is VERY nice, even at moderate power levels.

yes if you're eventually going to boost a 3" exhaust would be a very good idea to do it now.

I would be surprised if a 3" made more than 10whp on that setup. If you are going to run more boost later then, yeah it is worth it imo.