Is it an issue if my GPU runs at 99% load 80% of the time while playing games? I have a 7950 and while I play DayZ (horribly optimized) I sit around 99% load most of time and drop down to 60% load minimum. My temps stay around 60-70 ℃.
No there really isn't a big problem. Your temps are fine. If anything you should be happy that they are running at full load because a lot of people get worried about less than 80% utilization. I'd say it's working fine.