Like steelheadrob mentioned, I am running basically the same setup as you and him, with the stock exhaust. Tuner said the cats were getting hot after tuning on the dyno, mind you this probably built up some excessive heat with multiple dyno pulls. They suggested (should have listened) headers to eliminate the cats. At the time I didn’t want to spend the money for headers and just went with NEP cat delete pipes with stock exhaust. I HATED the sound of the exhaust with this setup with all the cats deleted thru the stock exhaust. So, I did Borla ATAK cat back with NPP, and added their mid pipe resonator. I think the resonator made the difference for me. I was much happier with the exhaust note of the Borla system and NEP pipes. It is very loud on startup, down shifts and when you stand on it. The cats really quiet it down. This is where my exhaust sits now.
Now looking back, I regret not doing the headers right off the bat, considering I have a set of 2" kooks no cats jet hot coated on order for the pursuit of more HP, so the cat delete pipes were a waste of $. My thought is with forced induction just about any cat runs you the risk of melting down and giving you problems. So, it’s a matter of $ and your personal taste of how you want the exhaust to sound. Even the high flow cats I think will eventually break down and cause issues, i could be wrong.
Good luck with your build, hit us up anytime, that is what we are all here for. This forum was so very helpful with my build. Research and ask questions.
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2017 1SS M6 Hyper Blue Metallic NPP, MMR 228 Z/28 replica wheels, Front: 20 x 9, Rear 20 x 11
Stock: 416hp/427tq, 12.21 @ 116.80
Modified 02/2019: Whipple SC w/ 3.500 pulley, LT4 fueling, NW 103 TB, Roto-Fab Big Gulp, Kooks 2" jet coated, full Borla ATAK exhaust, DSS axles, Gforce driveshaft.
Tuned by EFX Tuning 688hp/632tq
Best 1/4 to date: 10.705 @ 131.92