I decided to go full out and ordered:
Supersprint (non-powerloop) cans
Supersprint X-Pipe
I heard supersprint on several different cars at my BMW dealership and really like their house sound. I really like the sound clip of this setup on youtube but expect it will sound throatier, deeper like the the other cars I heard live vs. soundclip.
Also, I figure that this brand has enough equity that if I don't like it on my car I should be able to sell it fairly easily.
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2007 M Coupe w/NAV/Premium/Extended Leather, Clearbra, DICE, 4.10 BMW Motorsport Polished LSD, Active Autowerke Gen IV Headers, Supersprint Race Exhaust and X-Pipe, ESS Tuned DME, KWV3 Coilovers, Volk RE30, OEM Strut Tower Brace, Short Antenna, JL AMP, JL 10W7, Valentine V1.