I’ve had a similar issue quite recently as well.
Completely different problem from yours, I simply BSoD and reboot. No VGA/POST errors.
However, I think the problem I have is linked to yours as the BSoD I’ve been getting points towards a hardware issue (WHEA_UNCORRECTABLE_ERROR – 0×124) and it only seems to occur while playing GW, usually within 10 – 20 minutes. Nothing else triggers it.
Like you, I’ve done everything I can to try and pinpoint the problem.
Other games run without issue. Stress testing comes back without errors. Nothing else other than GW2 causes it.
What OS are you running? I’m running Win 8.1.