Well, Thursday no crash, Friday no crash, now I just had a lock up again. Not really sure what triggers it though... presumably it's not the drivers, and not directX. It's also no the temperatures, everything is as I expect from watercooling. CPU around 50-55°C, GPUs each around the 40°C, all VRM's are at similar temperatures. Could it be something with the power, in any case? Should I check the cables once again? Because I'm somewhat running out of ideas... and it does not crash with benchmarks or other games.