I guess my question would be why. Why would you want or need an 8th or 10th scale car to attain full scale speeds? Think about it, you've got a model car going the same speeds as a 1:1 car without the benefit of the technology in a 1:1. I've seen some full size cars get fairly messed up in a wreck at 70 MPH, I have to imagine cracking a R/C rig up at 70 MPH would effectively disintegrate it.
I think these manufacturers put speeds on their marketing for two reasons:
1. They know there are people out there who will buy based on speed and speed alone, no matter if that rig really can reach those speeds consistently.
2. They know that these very same people will probably never be in a situation where they will want or need to reach those speeds, even if the rig could consistently reach them.
I'm not impressed with a rig's top speed, more overall performance. My neighbor up the street, who's a real ass, has a Jato he keeps chirping about being so fast and what not. Problem is, the bonehead is always slamming it into curbs and tearing it up! He keeps wanting me to bring my MT out to race him, and I keep telling him if he can keep the Jato running for more than 5 minutes I will!