I'd just go with the CFM cat, that's what I have on my car now. I passed my emissions test with an ORP this year... no CEL and no inspections just a scanner.
I got a brand new OEM cat under warranty last year and the invoice priced it at $2500, it has 600 miles on it as it sits. Took it off to protect it and the O2's, if you know what I mean, and to get the ORP/HFC performance gain.
Fox Hound: Liquid Stang - Sniper Focus - Decoy Escort (or was it a Tracer...)