i have one ssd(optical bay 1) with mavericks and a second hhd(optical bay 2) with mountain lion installed in my mac pro. since i've installed macvidcards gtx 780 i cannot boot successfully from the second drive. on startup i hold option, select the mountain lion hd and press enter. after showing the apple logo with the spinning gear it gives me the grey screen of death. to troubleshoot i put back my old nvidia fx4800 and the computer booted up with the second hdd with no issues. i need to have a mountain lion boot disk because davinci resolve does not play well with mavericks. does anyone know how i can boot with the second drive and not get the grey screen of death? EDIT: See post #20 and #21 for the fix.