I noticed that as well. I even slowed the NA down and then it overtook the tubbys. Everyone knows NA's are faster 
Damn, I've been playing with the Tubbys - one I've setup to be as close to my own car as I can, calypso rot (German equivalent of same paint), fixed suspension, normal tyres. Shame I couldn't paint the wheels and V in black
I know for sure I've got rid of an NA before now thinking "won't need that, got a Tubby". Gonna have to go and buy one now. I'm guessing you can add a supercharger to it? That really would be a .orgster's dream car...