I ended up delteing my resonators...not the cats. Still have the stock exhaust.
IMHO, it did not make a lot of difference in sound. It is slightly more raspy, but really not a big difference at all.
I felt no difference in power at all. Hell, they are basically just a straight pipe with some hole in the walls for baffling sound. No restriction for flow in them, so I would not expect any hp gain or loss.
Tim (apparently likes "3" cars)
E90 M3 -- Current ride
2004 GT3 -- Sold
1997 M3/4 -- Sold
1995 M3 -- Sold