I am not sure but I just checked in C4 and got about 100 FPS in close range of the house with the most polygons, all normal maps applied, real-time shadow mapping, a parallel light and a point light:





I think this all depends on the scene management. In C4 you can use occlusion portals. So you can place a block inside a building and it will occlude everything behind it. So even a whole city could be done if you create small alleys and lots of structures blocking the view.
And besides that there is LOD. The lowest LOD has only 100-200 polygons. Assassins Creed has been built in a similar way.

Someone has to make a stress test