I've got all the latest stuff, GSM is standalone and works on 1.0 version of OPL, but whenever I try to use it with the beta version of OPL on every GSM res except the basic one on boot I get that screen
Latest stuff is not telling me anything.
Try to wrote e.g. GSM 0.38, OPL v1.0.0, OPL v1.1.0-Beta-1738...
Because a few hours earlier a new version (1740) of OPL has been released...
I am not sure why you want to use standalone GSM with OPL?
OPL has embedded GSM in which you can change resolution for GUI in Display Settings:
and for games in Games' Options:
Unless there is one resolution that is not available in embedded OPL and you need it,
but which one?