I have a Quat-D midpipe w/ DP ECU & airbox and partially cored stock cans, ceramic coated. I say partially cored because only the last maybe 2 to 3 inches of the inside of the can was removed; the main internal baffle remains. Cans were painted with several coats of Rust Oleum BBQ grill paint. I recommend this paint highly. It has a very nice even matte finish when done carefully with the proper preparation, and fairly durable.
After the shop tuned everything I can't really tell the difference in power delivery from stock ECU/udder & partially cored. I can't really say from a seat of the pants perspective if it's got more power or not. Maybe I'm just getting used to it.
However the sound is really cool. Got the carbon Termis that came with the ECU still sitting in the box.