I have investigated the graphics crashes a lot this evening with a savegame that shows the behavior when you wildly click on the minimap.
The savegame is in 1477AD researching Compass.
Killing all units does not change the behavior. It still crashes fast. So I think we can rule out units as a major source of the problem.
After removing all cities it does not crash any more.
Removing all buildings does the same.
Removing all world wonders or national wonders does not cause any noticable change in the crashing behavior.
Removing all buildings built after 1000AD means no more crashing but removing only those built after 1009AD I could still get it to crash. There are no new building types finished in that period (that have not been built before).
Removing all buildings that have a building type that is first built after 1000AD still causes crashes. Same for building types that are introduced after 600AD. Doing the same with 400AD still crashes, but not as easy.
That is as far as I got this evening.
So I think there is more than one problem source. Maybe too detailed models.
The culprits we seek are buildings that probably have a model, are first built around 400-600AD (some probably earlier) but mass built in 1000-1500AD.
Judging from some other reports some of them might go obsolete after renaissance.