Not sure what you are trying to accomplish will improve anything. If this is a dedicated cab, I don't see the benefit especially when it comes to fragmentation. Fragmentation only haves when there's lots of read and writes, but with the typical mame setup, once you have all the software load plus the roms. There really not much writing going on after that.
And with a ram drive, each time the system starts up, you will have copy the stuff over to ram, same more time lost than saved.