The problem with weight is that if you set weight something too heavy the vehicle might decide to submerge in the terrain/interior after a jump. I tried setting a truck of mine to 900 and I was experiencing that. Currently, I set my heavier vehicles to 600. Also, the proposed weight for the Blocko Sedan is unfitting, as 70's European/Soviet cars were much lighter than today's compacts.
Also, you have to remember that wheelspeed is like how many studs you cover in 1 second. So setting it to 64 would mean that you would cover the distance of 128 studs in 1 second, which would be way too fast.
What I would really appreciate in BL would be some kind of a gearbox. Currently, the closest thing we have is the C key, but sometimes it's not quite enough.