I actually noticed this during beta 4, but it was the first time I noticed buildings, on my new laptop, so I thought they just needed some optimizing, which would be done for the release.

I get a constant max framerate (limited to 90 in my case, for example) over all the map, on a bare ground, units for example are ok. But as soon as a small 3D object enters the field, it decreases. A tree in the corner? 45 fps. A city (not a big one, just the first settlement) visible? 15 fps.

I tried to change the various settings, deactivated soft lighting, AA, shadows, resolution, it's still doing the same. It works good on the cloth map, without a problem, though, as there are no such elements.

Now I would understand such thing on my older laptop, but I'm surprised to see this on the new one. Specs:

Processor: Intel(R) Core(TM) i7 CPU Q 720 @ 1.60GHz (8 CPUs), ~1.6GHz
Memory: 8192MB RAM
Video Card: ATI Mobility Radeon HD 5870
Operating System: Windows 7 Home Premium 64-bit

So I'm guessing there is somehow a problem with drivers (though latest ones from ATI), or at least some incompatibility somewhere. Because the objects are nice, the cell shading effect too, but it's hardly something to bring this computer to its knees.

ps: I understand that a game like this doesn't need to run at 90fps. But 15-20 is actually unpleasant on the long term.

Edit: To make a complete (more or less) analysis, I tried at a high and low configuration, similar effects:

LOW Settings:

- Video Configuration

- Over a city: 20 fps

- Without objects: 138 fps 

HIGH Settings:

- Video Configuration

- Over a city: 18 fps

- Without objects: 80 fps

So it doesn't seem to be related to the video settings. I also tried windowed, same.

It is really related to these 3D objects, as shown by these two other screenshots:

- Full zoom, empty ground: 99 fps

- Same place, just a bit higher to have one tree in the view: 29 fps

So far, the only thing which seems to improve performance is to force the game to run only on one core (physical one, so two virtual cores on Core i3/5/7), as suggested by thebigJ_A in this answer.

It should be the other way around, clearly, so maybe it's giving a hint on where the problem could be. Note that this doesn't solve the performance problem, there is still a big decrease on framerate when passing on cities, but less than when the game is authorized to run on all cores. I noticed however that doing this since the 1.05 version makes the sound choppy, probably because it was expecting to run on a different core to begin with.