I have problem with some models - when they are rendered, fps is going down (even from 60 to ~3). They don't have much poly (exemplary mesh have 564 tris and 4 parts). Some others models have much more polys (e.g. mech) and there is none fps drop.
What is strange - in WE scene with this models have 80 fps.
I'm running low details and simple rendering mode both in WE and game. What can be the reason of such case?

how many of these models do you render?
are you using Frustum culling?

One such model is enough to slow down game.
It's all about static objects, so I don't know. But there is difference if this model is inside cam view or not.
I noticed 2nd strange thing - if I use zoom fps is going to normal value (~60, zoom is ~same as in BM).

maybe the total amount of memory exceeds your GPU memory and DirectX needs to dynamically swap the textures/models.
What GPU do you have and how much RAM does it have?
you can send me that model so I could check it.

Model
I have R9700TX (128 MB).

I'll check the model, but is possible that the problem lies in low memory.
You can try setting smaller resolutions and check if problem disappears.

Now I use 800x600 windowed. Try this model + some other, if it's alone on scene fps drop is small.
And don't test it in WE - there is no problem...