I too am using DOS, arcadeos and MAME. I don't recall which version of MAME it is though.
I also switched to a 1gig compact flash card and an IDE adapter. There was no noticeable change in load times between hard drive and CF, and having no moving parts inside my cab (well, there's a fan in the power supply and on the CPU) make it all the more stable.
I'm running one of those tiny VIA Epia motherboards, and it's got enough speed to play all the classics that I'm interested in running.
If you use arcadeOS as a front end, just be aware that it takes a bit to get used to configuring it, and there's a bug that I'm trying to track down that pops up when I add a new game to one of my custom lists.
If you're using an arcade monitor, you will also need a config.sys driver (arcmon.sys iirc) to drive DOS at the proper refresh rate.
I've been really really happy with DOS and MAME on my cocktail machine. Let us know if you need help!
-jeff!