MaimRecoil & ShanMan, there are many options that could make the video card an issue. It could be just the changes to the default settings. Just to name a few.
D3D vs DD vs no directX:
Mame's default method was DirectDraw up to 0.106, and changed to direct3D from 0.107 on. If the card sucks at d3d, use dd. But the default settings now favor a d3d tuned card.
resolution:
Mame's default method was to switch resolution to near the original. OTOH, the current is to keep the desktop res and with d3d stretch to the bigger res. If the card isn't good at that high a res, make mame use a smaller res. Again, the default settings now favor a higher res tuned card than before.
overlays/bezels/art:
Mame has increased the art features. By default these are all enabled. If the card can't handle the high res art rerending or memory size, disable this or delete the art files. Again, the default settings + having the art files can make a huge hit on old cards.
None of these slow downs are part of the emulation of the original hardware, but to most users, the slow down doesn't matter if it has to do with emulating the game or drawing on the monitor, while to the developer the two are very different.
And older versions that didn't have these features or, if did, had different defaults, will be able to use lesser video cards without slow down.