Hmm, swap the res?

So my car is currently running MSDS headers/Y to a stock cat with 10K on it and a stock SVT catback with around 5K, both look pretty much brand new, though I might get a trubendz test pipe at some point. The sound right now is awesome, deep below secondaries and loud and aggressive after, but still (and this is a plus to me) relatively quiet on the inside, even cruising at 65-70 on the highway, unless I pause my music and have the window down slightly I can hear it, but subtly with no rasp/drone.

But say I wanted to go a little bit louder, and replaced the res with a straight through design, how much louder would it get? How would interior sound levels be? Would there be any perceived added rasp or drone, specifically at highway speeds since in daily driving, unless I'm driving spiritedly, I shift around 3K? When I do get a test pipe, will it rasp/drone then? I understand it's difficult to know exactly I just wanted general opinions on the subject

Thanks for the info guys, just wanted a little info with my on-the-cheap exhaust.

Do you have a intake? If you want to hear it in car and a little louder, i think a intake will be your best bet.

I'm running an SVT intake with a K&N, it's not hooked up to fender ducting.