There is no such thing as "scale speed"......
here is the simple understanding:
100kg of sugar and 10kg of sugar, which one is more sweet ?
ditto with a real car traveling at 60km/h and 1/10 or 1/12 scale car travelling at 60km/h, which one is faster ?
If you insist to use scale measurement for "real world" situation, then you can see real car such as dodge stratus or mazda 6 traveling at 600km/h
Of course not right?
Btw, aerodynamic body is important factor to get stability on the straight at full speed. I innocently enter 8T motor modified race with mini cooper body
and it was awful. The car is not stable at all on the straight. I end up loosing two set of suspension arms, one turnbuckle, damage chassis
So after the race, I follow the other people setup: mazda 6, dodge stratus, nemesis. It is huge different and I'm happy.