you should do the masseratti too, unless you tune down the pace of the other cars too to be on pace with the masseratti , cause you said you did not do the masseratti cause kunos car already in game.Those are average speeds, not topspeeds. Obviously quicker laptimes = faster average speeds.
Anyway, please if you want information about the MC12, or if you think something is wrong, or whatever else, use the appropiate forum: http://www.assettocorsa.net/forum/index.php?forums/physics-bugs-issues.15/
This thread is to show/discuss about our cars.
so what will you do with the physics?