Hi Shift,
I took a look back through your other threads.
Given that you're using a workstation graphics card instead of a gaming card, and the type of issue you're having, my guess would be along the same line as AmShaegars, towards an overheating issue.
Although most workstation cards can run games, their architecture is built for a different purpose and in some cases they can get stressed out more than you'd see in a normal video card.
You may want to try double checking your temperatures while in game and see if you're spiking at all beyond what the card (or possibly the processor depending on how high your ambient temperature gets) should be running.