I'm exceedingly interested in the 3rd and 4th part of your mod. Just wondering though:
1) Are tyre sizes and hence diameters corrected? I messed around with some gear ratio changes and still could not get the right rpm to vehicle speed for some cars here and there even with the exact gear and final drive ratios. Can't remember which cars had the problem though.
2) How did you manage to fix the VAG speedometers? I was thinking of trying to add another 'speed to needle degrees' line to the cockpit definition file to see if it's possible since higher speeds use another speedo scaling. (Some cars even had 3(!) different speedo scales.)
I believe the Mitsu Evo X, Corvette Z06, Seat Leon Cupra, Gallardo LP560-4 and Bentley Conti SS also suffer from some speedo inaccuracy.
Hope to try out your beta soon.