Here's the link to the CP i was talking about
http://www.gamesx.com/stick/Do you have a specific model ... mini-itx is a quasi standard, not really a "type" or "speed" mobo.
Linkage? WHICH itx board where you looking at?
The general guideline is that a 1.something gigahz machine (regardless of form factor -- unless it's a real dog) should play I dunno 97% of all mame games well.
Some games will play choppy no matter what, at the moment. But I got to imagine MvsC, SFII etc all should run swimmingly on anything remotely modern/recent chip speed.
You can of course get by with less... and still be happy, but we're speaking in very broad general terms.
Rampy