For those that have asked me about the quad tips, here is a link to what I have. I currently have them mated to M Performance mufflers, but previously had them mounted on my stock mufflers as well. They fit perfectly with the stock 550 diffuser, or any aftermarket diffusers made for a 550. I am running the M Performance diffuser made for a 550 (my car is a 535). Alignment will be off with an M5 diffuser.
http://www.ebay.com/itm/PORSCHE-997-...BYSQTa&vxp=mtr