7 vs 8 other the the UI which is easily reverted or tweaked either way the only difference I really care to note at this point is the DX11.1 being windows 8 exclusive thing but again I am not sure that will matter for many years yet.
Faster is fairly subjective and varies wildly between what is a cooked test, what is a test that only matters in a lab, what is the fault of drivers (either being badly written and crashing but maybe gaining a few extra FPS here and there* or being unoptimised seeing a loss of them) and there is always the "what is it like on a machine after 6 months of general use (after you have installed all your printer stuff, added stuff for your phone and watched the drive fragment up a treat).
*for my money this is all games graphics cards but CAD graphics cards and their drivers, which are designed for stability, are not that good for games so stick with the games stuff.
By and large the 64 bit versions of windows dropped the 16 bit subsystems but most people had been on dosbox or actual vintage machines for old games for years now anyway, many DOS era games you might want to play have been remade/had source code released.
For the "post dos" stuff it always fun to try to get working as game coders have some very interesting ideas and newer versions of windows are trying their best to be half secure and streamline their coding/processes. Granted other coders have some very interesting ideas as well but games are not immune. Still dosbox, Windows' own backwards compatibility options, various implementations of WINE and co do well and I reckon virtual machines might soon be there as far as 3d goes (as it stands it is at the "give it a go" stage, especially if it is a not an old FPS/twitch game).
Equally it is always worth checking forums and developer websites to see if people have released patches, workarounds.
The short version of that is - windows 7, windows 8, windows vista or possibly even windows XP - you are equally screwed either way when it comes to the older games but you can usually get around it if you try.