... I really don't care for the sound ...
Putting headers on an otherwise stock Gen 1 CTS-V (LS6) plus a tune netted guys between 20-25 rwhp "back in the day." I never baselined my car when stock, but most guys (again, "back in the day") were seeing about 320-325 rwhp (stock LS6) on DynoJets. I did dyno my car (DynoJet) after the headers and tune and saw 350 rwhp (SAE corrected), so that seemed to be in agreement with others.
If you're already at 376 rwhp, I'm not sure what effect headers would have for you. They do sound borderline uncivilized, so I can understand you not caring for them.
I haven't read much about ported heads. If you do them, be sure to post up a thread on your results.
Just to belabor it a bit more, my theory is it all depends on what it is about a particular engine's layout and the air flow into, through, and out that's dominates as the limiting factor. There can be only one at any one point in time, though everything may be in close balance so affecting the one that limits you may not get you much. Could be too much turbulent flow in the heads or some other kind of restriction in there that's choking your motor. In that case, porting will have a beneficial effect. In my case right now, I know where the restriction is (78mm TB), but I've chosen to not pursue modding it. It would be my luck to trade off the reliability I enjoy now for a "walk home" event. I'm getting too old for that.
