I had a 93 rx7 before switching to a string of 4 m3s....currently on a e90. With very simple mods (intake and exhaust) and stock suspension it was around 300hp and was faster than my e46 which had basic suspension mods (springs/shocks/sways). It wasn't a R model but since it only weighed 2800, it flew around the track with very little wear of the brakes and tires. Looking back, it was the BEST track car I've owned to date....and perhaps the most affordable. The seats were snug, the shifter is best in business and most of all, it was light and tossable.
My engine "blew" at 80k when a small radiator clamp came loose and I lost all fluids. Unfortunately, at 140mph, couldn't see the steam coming out of the hood until turn 1....and by then it was too late.
When I take the e90 to the track, I expect that the power advantage plus more updated suspension will help this car finally beat the ole 93s time at summit point. At tracks like lime rock, I would expect the rx7 to still be faster than any m3s. Feel free to PM me for any q's or details.