I have just tested a few games which ran much slower than 100% speed and all seem to run 3-5% quicker.
It may just be a coincidence but can anyone else see if they get the same results. i was lucky my previous results were on the sdlmame wiki http://wiki.maemo.org/Sdlmameso so i had something to compare with.

games tested:-

marble madness
outrun
afterburner
ghouls n ghosts
r-type (the speed of the game still boosts from 32% to 85% after 30 secs of the rom running)