Do what I am doing/have done. Going to muffler shop next Friday to install remaining parts. I had them cut out the secondary cats, and installed Magnaflow mufflers in the rear. Next friday, swapping out the OEM x pipe with a magnaflow one and replacing the resonators with something a bit more friendly. Also getting my springs and pulley put on. There will be nothing left of the OEM exhaust. In about a month, deleting the primary cats. Cost for all this work? Less than 1000 bucks, same stuff as the overpriced xpipes.
2008 (07/08) E92 M3 BPM Stage II Tuned by Mike Benvo, 6MT, Turner Test Pipes, Magnaflow Custom Catback Exhaust (Magnaflow X Pipe, secondary cat delete, Aero Resonators and Helmholtz Chambers),Vorsteiner CF Lip, Hamann Style CF rear diffuser, CF Rear Decklid Spoiler, BMW Performance Kidney Grills, CF Side Grills, OEM GTS Wheels, K&N Drop-In Filter, GP Thunder 8k Angel Eyes, Painted Reflectors.