It just struck me as strange that Dinan had prob lems, but Turner doesn't with 3.91 diffs.
WRT speed in gear, there is a site with a calculator, but I have posted the forumla on this board, and also did my own Excel spread sheet to calculate max speed in gear based on RPM and diff ratios, considering the tranny ratios fixed.
I was surprised to see that the M3 would hit well over 60 in second, and even just go over 60 with a 3.91.
'95 Alpine M3 LTW
'00 Dakar M Roadster
'02 Topaz M3
Red/White SRF #4 (Chassis 561)