Followup to my first post - got the 3fps bug after 4 to 5 hours.. still seems more stable than before. Not a solution but a promising development! Thanks guys!
EDIT: Alt-Tabbed to write this - went back to game and it recovered!
EDIT #2: KOTH round finished, tried to load next mission and Arma crashed with Unable_to_init_DXGI. Had to Winkey+tab to bring up task manager in a separate desktop session to quit.