The OS isn't so much the concern as the emulator.
Vantage, RAINE, Kawaks, etc are all much faster than MAME. If the games you want to play are supported by different emulators, try them out and see how you go.
RAINE in particular is very interesting. The supported games list is growing at a pretty crazy rate, and folks like Haze are converting MAME drivers across which is brilliant. Plus RAINE is licensed under a much friendlier Artistic license. MAME's license makes the hippy in me cry.
With that said, if I build a system low on RAM then I'll use Linux + SVGALib, as there's much less memory consumed by the GUI which can then be used by emulators + games instead.