Strange flickering in my game all of a sudden

I wouldn't worry about overworking your GPU, exactly; it should be able to handle running at close to 100% load for hours at a time as long as it can adequately cool itself. On that note, if you remember hwinfo, you can run that while you play to see the card's temperature and core load, along with a lot of other stats that you probably don't care about at all.

I was more saying that if you increase the load on your GPU to the point that it's running at or close to max capacity, you might notice fps drops in-game. But as long as the card isn't overheating, there's no danger in experimenting.