some versions of MAME play some games better than others. It's true. It will always be a moving target, so you might as well jump in now and if there are games you can't play, then hunt around for specifics. Most of the issues were the increase in processing power and graphics display power required to meet some of the new audio/video syncing the developers put in to improve the emulation quality. If your machine is capable of running maximus, then it is absolutely powerful enough to run old games even with the new performance demands.
as for high scores, check the stickied posts in this very forum. you will have to recompile mame to add supprt for it, but that's easy to do too with the mame compiler.