I don't have comp mufflers but I am currently in the process of having M6 mufflers installed on my car. With my Vorsteiner diffuser, I really wanted 4" tips. I am planning on keeping the valve in place on the mufflers so I may need to have the shop cut the inner "non-valve" outlet pipe and install an s-pipe. I dropped the car off yesterday with the shop with the following tips. The burnt blue look may or may not be your taste but I like them so I hope nobody gives me any grief. I love the glossy carbon tips too but I couldn’t find anything that would work in my situation.
https://www.ebay.com/itm/2X-Blue-Bur...72.m2749.l2649
Do not buy these ones. They are 8" long (despite their posting incorrectly indicating they are 9" long) and they will stick out way too far.
I just ordered the ones below and plan to have the shop cut them off right at the weld and have the shop weld them on, which will help to maintain the valve.
https://www.ebay.com/itm/Dual-4-Quad...53.m2749.l2648
Good luck and keep us posted on what you go with. Hopefully I’ll be able to post up some pics next week after the tips are delivered.