I've been able to get my car to 150mph, as indicated by an independant GPS unit (New Road Angel, if you're interested). Speedo read something like 155mph. I only tried it once, my friend got a pic on his camera phone... I should find out if he's still got it.
Don't know if the car could have gone faster... I was too scared to! I doubt it though since it's already like 3mph over what the speed regulator should be set to (147mph in the UK I believe). My needle was roughly in the same place as yours Shaun(Rabbit222)!