OK, I've run some tests. I turned the graphics right down/ off and tried it in windowed mode for better monitoring.
The thing that jumps out is the fps- regularly over 200, often hitting 260+. Is there a solution?
Temperature stays mostly at about 75 deg C/ 170F with occasional peaks to 81 C / 180F; Skyrim runs at 81 C without problem.
The game itself seems to run OK with a created family, but I wouldn't know if there could be situations I haven't tried yet which could give problems. FPS drops when the SIM is doing something, and rests around 220.
The game always crashes during the second SIM in CAS, and I'm not sure why that should be. Surely doing the second one isn't more power hungry than the first? The fps seemed higher during the second SIM; it varied wildly, and crashed at fps=237 for reasons that seemed unclear.
Thanks again.