https://bugs.freedesktop.org/show_bug.cgi?id=109445
--- Comment #4 from Bas Nieuwenhuizen bas@basnieuwenhuizen.nl --- since you mentioned your system does not respond to ping or ssh I wonder if it is actually not a gpu problem, but more generally being under load.
maybe try idle=nomwait? That solved regular lockup problems on my 2500U.
At the same time locking up consistently within 5 minutes sounds pretty bad, so I'm not sure this will fix it.