Fabspeed makes a secondary cat delete with or without resonators which is a few hundred cheaper than the Challenge. You can also find a shop to cut out the secondaries and replace them with straight pipe. I think that is the direction that I am going to take.
E90 M3 Jerez Black/Bamboo Beige 6MT - BMW CCA
Dinan Rear Exhaust, Secondary Cat Delete, Dinan High Flow Carbon Fiber Intake, IND Painted Reflectors, BMW Edition Grills