Try to stay clear of Furmark as a whole. It pushes your card to an unreasonably-intense load that can possibly harm it. Run Unigine Heaven several times, run a few graphically intense gaming benchmarks, or just play a few graphically intense games for awhile to determine stability (watch for artifacts and crashes).
Furmark generates too much heat in my opinion. I'm running OpenCL compute operations on my GPUs and they're locked at 100% 24/7. This load is greater than any gaming load, but the temps stay reasonable. Yet after five minutes Furmarking, my temps exceed what they do in a real-life full-load situation after 24 hours, so in my opinion, their burn in test burns a little too much.
EDIT: I didn't mean to imply that you had done anything wrong, plenty of people use Furmark and like it, I'm just not one of them.