2 matches on SR, 2 video driver crashes - unplayable

I can't get through 10 minutes of the new SR without having my video driver crash. This results in a black screen for 10 seconds followed by severe corruption (distorted shadows appearing as lines across the screen, epileptic colours when opening the shop).

This is not my video card giving up the ghost because every other game works fine, including ones that are much heavier than League + video card RAM test reported no errors. Shadow of Mordor with all options cranked up and Unreal Engine 4 on the second monitor = no problem. League custom match with old map = no problem. League with new map = crash.

R9 280X, latest drivers, not overheating, not even exerting the fan. So much for League of Legends. :(