Where did you get the 65kph limit? On the mech builder I use I can get it to 75 with a regular engine, sure that engine is like 45+ tons, but its not xl. Mabye I am looking at one that uses tech past 3049?
max speed with a 400 engine is 64k/h for an atlas
10.8 x 1.5 x 400 / 100 = 64.8 k/h
whatever you are using is wrong and stupid