I hear that every five years or so, and yet someone always manages to find a way to keep Moore's law rolling.
Moore's law has nothing to do with clockspeed. It states that transistor density will double every 18-24 months.
http://en.wikipedia.org/wiki/Moore%27s_LawTransistor density has nothing to do with clockspeed.
And at any rate, there's been a theoretical practical limit of clockspeeds being 5GHz for some time now (well over a decade). Anything faster than that becomes impractical due to electron loss on any semiconductor (eg: silicon) or conductor (copper, aluminium, or whatever else).
Fibre-optic switching faster than 5GHz would be the only sensible alternative, but you won't be seeing any processors based on that technology for some time, nor will they be anything like what we use today.
On the topic at hand: MAME is not very well optimised at all. And that's fine - it's not intended to be. MAME is designed entirely for accuracy and documentation. Playing games through it is merely a "pleasant side effect" according to the developers and designers.
If you want to play more recent games, you'll have to look at other options. Either different emulators (Kawaks, ZiNc, etc are all faster than MAME at the expense of some accuracy). Or alternatively look for a console port. Unlike the old days, console ports of modern arcade games are not bad at all. Gauntlet Dark Legacy has been ported to XBox, PS2 and GameCube. Consider putting any of those inside an arcade cabinet and playing the game that way instead. Plus that way, the developers actually get rewarded for their hard work, rather than you playing the unlicensed copyright games for free.
http://www.mameworld.net/maws/romset/gauntdlScroll down to "Additional Information" and look for the part that says "- PORTS -". Do the same for any other MAME game, and consider buying a console port whenever possible.
Might I remind everyone here that the only reason we have these games to emulate is because the people making them can afford to do so. Please consider buying games as frequently as possible, even if they are on offer via emulation.