Civilization 5: How long does it take to get to the next turn, considering a large map, and maybe ith autosave on/off (if that even matters, i'm not sure).
Starcraft II (with medium details, but with high settings for the CPU, like physics); a replay is a good test because it can be repeated, altough it does not stress the CPu as much as a real match.
I'm not sure if you know the software, but Ansys is a great software to stress the CPU. It's a engeneering simulation software, look up some images on Google. It takes an awfull lot of time to simulate stuff on a somewhat complex model, specially with a fine mesh and simulating a lot of things (heat transfer, elastic/plastic deformations, and so on).
There are other similar softwares tho, I'm just familiar with this one.