I also had several cases failing orthos and passing memtest. I used that as stable because if they pass memtest they never gave me any error in real work/job/gaming etc.
It's always good to have another pc nearby, i try my rams at my brother's pc if they give me any trouble to see if they still work normally. It would be wise if you could to do the same, perhaps at a friend's or so.
Do tell if you seen any progress, i am really eager to see what could be the issue.