Z4 non-M sports suspension is based on the E46 non-M design. Struts, springs, shocks, control arms...etc are all interchangeable between them. The Z4 M suspension is a hybrid between E36 M3 and E46 M3, with the front suspension parts being re-designed E36 M3 parts, and the rear suspension parts being redesigned E46 M3 parts. The swaybars are from E46 M3 as well (rears are E46 M3 CSL bars).
As for comparison, the non-M Z4 will hold its own, but the MZ4s have stiffer springs and higher damper rates, plus the MZ4s have more camber up front. The lower control arm is from the E46 330i with Performance Package (ZHP). The major difference will be the fact that the MZ4 has a tuned limited slip differential while the Z4 3.0Si has an open diff, and the M has servotronic rack-and-pinion steering instead of the non-M's electronically assisted rack-and-pinion steering. The M also has a quicker steering ratio.
End result, is that on the track the M has a much higher threshold, with quicker turn-in feel. But you will not be disappointed with the 3.0Si coupe, it'll likely hang at most tracks with the best of them. 265HP on a 2,9xx lbs frame is going to make a very capable car on track.
http://forums.bimmerforums.com/forum...d.php?t=844305