You can get some nippy 125's that would wipe the floor with even some super cars to 60... they're just very limited top-end.
I've got an RX125 (the crosser version of the Aprilia RS) and it's the same water cooled engine. The bike has been wrapped around a few tree's in it's life and previous owners have rebuilt it and bored out the engine a little (god knows what to).
It'll do about 95 before starting to sound a bit rough and it backs off the power and wobbles a little due to how high it is off the floor and the huge forks and lack of aerodynamics but it it'll get to about 75 fairly quick.
The RS though is a much more stable bike and doesn't wobble when you're hitting quicker speeds. A friend has got one that I know can do 110 and it gets to about 100 pretty fast and it's pretty much stock.
I've had an RD, KMX and TS 125's and they've all gone fairly quick for what they are. Had some though that haven't. RG, CG and all my older 50cc's lol.