I have a 3" system with H-pipe and spintech mufflers. I have cutouts in sort of a max wedge style, so the flow when they're capped isn't optimal. Every time I've done back to back tests, I've picked up 2-3 tenths, simply removing the plates.

Now, I haven't changed the jetting since the motor was dyno'd, and it was dyno'd at sea level, 70 degrees and open exhaust.

Fontana, where I usually run is 1100 ft, and DA is always 2000+, so I'm sure it's running fat anyway.
I haven't worried to much about jetting as I'm not legal for 9's and short-shift it to stay in the 10.0's anyway.

Best DA I've ever experienced was new year's day this year, 1700 ft. Went 9.92

Your results may vary...