Yeah I think adamlee is spot on, its not very normal. However, as long as the computer doesn't turn it self off or start thermal throttling, it's fine.
I don't think there's a point to reinstalling Windows 7 unless this always happens however, so you should be fine.
However, what temperatures are you getting on load? This could also be a stability issue due to temps (I doubt it however).
On an other note, I am very jelly of your 780 setup.