depends on brakes aswell, an m5 will have better brakes than most cossies, even with the extra weight, the 400kg may help it get from 60-130 quicker, but after that aero comes in force

at vmax they dont brake so late that they risk crashing, the marker isnt at the very end, normally when people go with the mags use the maximum distance they can get away with to give them the best chance.