I've had the Fabspeed resonated xpipe w/Fabspeed high flow cats now for almost 8-9K miles and I'm using the supplied O2 extenders. Driven in temperatures ranging from 10F to 90F at loads from a track day to normal day-to-day driving and the CEL has not come on at all. I have a Powerchip stage I tune (which does NOT remove the CEL, stage II does).
Everyone keeps saying it will come on eventually, but I doubt it at this point.
2008 E92 M3 | 2007 Honda S2000 | 2001 Honda S2000 | 1997 Turbo Integra