This may be neither here nor there depending on your financial position, but I think the PC running your arcade cab should be as smoking as possible. My cab, for instance, will have a steering wheel on it. Not to say that Outrun and Spy Hunter aren't fun games, but I want to be able to fire up Colin McRae 3 and Driver now and then. For those (and any game made in the last couple years) you're going to want a decent 3D chipset. Luckily I'll be using a TV for my monitor which restricts me to 640x480 resolution so the 3D chipset doesn't have to be THAT decent. I just hope developers of 3D games don't start dropping support for 640x480 any time soon.
The same advice goes for all modern games (that are playable with arcade controls), of course, not just racing games.