I ran TTI open step headers on my race car for a few years. Installed a 3" X-pipe and the Dynomax Ultraflos and actually picked up a little ET, especially after some carb tuning. The X-pipe probably helped the most, but I'm sure the mufflers didn't hurt at all. The only downside was having to take 60lbs out to bring the car weight back to the minimum race weight.

I've gotten many compliments at the track. But the engine doesn't stay in the midrange very long so I don't know if there would be any drone at any particular rpm.