Scale Speed isn't/wasn't the issue of this thread...and there is NO such thing as "Scale Speed" , but moreso scale reaction to speed. If you were to actually be able to Scale Speed, you'd also have to scale gravity & air density.
As far as the Scale 'weights', what types of cars are you referring too?
A Nascar Cup car specs are
Weight: 3,400 pounds
Wheelbase: 110 inches
That would be a 3.4 lb car (1/10th scale...true weight) and the wheelbase would be 11.0 inches.
My Oval Pan car runs a 10.5 - 10.8" wheel base, but is closer to 44 ozs. which is what 2.75 lbs...which is closer to the weight of a short track late model like a ASA car.
TC's are quite heavy if that's what we're talking...