the initial boot will be at 31k. To stop your monitor being possibly damaged with the wrong sync rate, you need to use a JPAC (from ultimarc.com) which will block the sync until the software changes it to 15k.
To boot into one game, go into the file manager from the groovyarcade setup, then navigate to /home/arcade, then cursor down to .xinitrc
This file is used to load the frontend UI or game menu. press F4 to edit it. The last command in this file will be the something like 'advmenu'
change it to load MAME or whatever else you want to run.