the 680 at lower resolutions
will be spitting out frames much faster and be putting more of a load on cpu. i put that out there not because i would suspect it will be a problem but that increasing the resolution and details will alleviate the restriction. but really i sould relize you're going to running everthing maxed out; its a SIX-EIGHTY we are talking here.
EDIT: ooopss sorry you did not refer to that specific model.