gpio speed

Are there still wait states for other reasons?

Not that I'm aware of.

Also, if you just want a crazy fast clock, looks like you can turn on the 'Microcontroller clock output' :)

can I overclock it by setting the PLL multiplier to more than 9x?

Possibly, yes :) I seem to recall that using setClock on the F4 I tried I could get it from 84 Mhz up to 120 or so.

I believe there may be other registers (there were on the F4 IIRC) that allow you to tweak the core voltage up a bit, which will let you hit the higher speeds.

Having said that, you may need to do some fiddling if you want USB to stay working :)