So assuming u forgot the [ sarcasm ] tag on the last one, it seems to be a combination of atom + game + as mame gets bigger it gets slower.
However, i must say that on same computer when loading .146 rom with mame 0.146, the frame rate is 95%, so the version does have make a difference.
I have also found a lot of working roms that stopped working in 147. No replies to my thread on that, however it is getting annoying switching from one front end to another for a bit of mk3