The screen does black out after a few mins. Another interesting thing about my other rig that didn't drop at all is that I unplugged the monitor cable from the GPU so I could use it on my Asrock H81 board that do need a monitor plugged in to start. Don't know if that has anything to with it, but... let me do some test about that monitor being powered off by X scenario....
No wonder I didn't experience the drop, my rig has no monitor connected.
the drop also happens on some of my rigs without a monitor attached. all rigs running 290 and 290x cards.