mafje If your computer works fine with one GPU but not the other, than the problem is almost always going to be the GPU itself. It is of course possible in theory that the game can't run on this family of graphics cards, but I haven't seen any other reports of unsolvable Sims 3 problems on any card in this generation, and it's very unlikely that compatibility would break between new GPUs and only one older game, as opposed to a family of games. The fact that the game works slightly better at a lower resolution and refresh rate, and therefore a lower workload, also points to the GPU.
At any rate, I think your next step is to test the graphics card in other contexts. You can download the free 3DMark trial from Steam and run Time Spy a few times, back to back, to see what happens, but even if it doesn't crash, I wouldn't consider that totally definitive. I would suggest running another program alongside Time Spy that tracks GPU temperatures, for example hwinfo or GPU-Z, so you can see whether the core or hotspot temps are getting too high. Hwinfo in particular tracks a LOT of data, and it might pick up some other GPU sensor with values outside of what is safe or allowed. You can also test while trying to run Sims 3.
Separately, it's worth disconnecting and reconnecting the power cables feeding the graphics card, at both ends if the PSU is modular, making sure they're fully inserted and the ports are clean. Bad power delivery could explain the problem too, and if the cause is not the cables themselves but how they're inserted or a contact on the GPU itself, you might not see an issue when swapping cards.
