What version of MAME are you running?
I'm running MAME pp 0.109 and throttle seems to work fine?

I didn't know there was a problem - but I'm fairly certain game speeds are correct? (at least nothing hugely sped up or down).
I'll have to check my mamepp.ini file on my cab later, I *think* triplebuffer was giving me grief at some stage, so I'm not sure of my settings off the top of my head... if that's any help to you at all

From memory I remember some talk of triplebuffer affecting throttle?? So maybe try toggling that also?