I think a lot of the folks doing the cut-outs (like the above displayed red GT) are maybe trying to do a throw-back to the old Mustang GT's of the late 60's that had the exhaust integrated into the rear bumper. Aside from making things a total nightmare to line up correctly and avoid making them stick out too far or clatter against the surrounding bumper area, I've noticed in every case that they tend to gather a lot of soot all over the bumper - something about the difference of airflow in that area, maybe a lower-pressure area, since the tips aren't in a path of wind that can sweep it away, I dunno. I see it all over the place around town on pickup trucks with fiberglass/ABS roll pans and big ol' honkin' 3" or 4" tips poking out of the back.
The only way I can see it as being somewhat decent looking is if one were to ... 1. Keep the tailpipes flush with the bumper and not have them extending more than 1" outward, 2. "Frenching" the surrounding cutout, or at least making it LOOK like someone didn't just take a hole saw or Sawzall to the rear valence, and 3. Use a square-shaped tip instead of a tiny little 2" round exhaust tip (or, worse still, a gigantic 4" hole), as it would tend to match the lines of the body style a lot better.
FWIW, if I hadn't already blown the money on stainless Dynomax tails and spent three hours fighting to get the stupid things to line up properly (no longer do they have such a severe upward slant, and they don't rattle against the bumper), I would've sooner gone with a side-exit setup with some slant-cut square tips. Leaves plenty of room for rear suspension mods that way.
The only way I can see it as being somewhat decent looking is if one were to ... 1. Keep the tailpipes flush with the bumper and not have them extending more than 1" outward, 2. "Frenching" the surrounding cutout, or at least making it LOOK like someone didn't just take a hole saw or Sawzall to the rear valence, and 3. Use a square-shaped tip instead of a tiny little 2" round exhaust tip (or, worse still, a gigantic 4" hole), as it would tend to match the lines of the body style a lot better.
FWIW, if I hadn't already blown the money on stainless Dynomax tails and spent three hours fighting to get the stupid things to line up properly (no longer do they have such a severe upward slant, and they don't rattle against the bumper), I would've sooner gone with a side-exit setup with some slant-cut square tips. Leaves plenty of room for rear suspension mods that way.
I'm feeling sooo many emotions right now, hold on...
More power to ya 
