I passed my test in 1974. so my Highway Code is still in Latin. I've just checked on t'interweb, and the stopping distances appear to be the same as they were then. This is despite the fact that, when the Highway Code was introduced, most cars had drum brakes and ran on cross ply tyres. Since then, most cars have a servo assisted braking system on disc brakes, with radial tyres, and also ABS, EBD, etc. Tyre technology has also improved dramatically over that time.
I still remember the breaking distances, 75 - 315 feet, but that bears no resemblance to reality these days.
What this has to do with speeding courses is, at best, tenuous, but with modern technology, it's never been so easy to slow down and stay within the speed limit. :-)