The problem is very interesting, because for the G91R4 (3D design unfortunately currently still) I had discussions with the person who did the 3D model. 3D modelers often lose a lot of time in an attempt to maximize the number of vertices, but actually I think it's more important to spend their time on other things, such as the optimization of the surfaces, as they often appear to be "edgy" with an effect really far from reality.
I wanted to do a test with a sphere generated with the "wings-2.0.1". Initially the ball had 512 vertices, then, by pressing the [s] (smoothing) I increased the vertices.
Any increase export vertices in OBJ format and then, using Blender them esportavo format .ac (It's a pity, for FGFs, do not use a more common format).
I have included the files generated .ac, in the folder UFO / Models. I positioned the UFO in a point of the scenario (I was interested in making a test in real conditions) and I activated the advanced weather, trees value 5, highest possible quality with ALS active.
These are the results:
My system is:
GPU GeForce GTX 870M with 6GB RAM Video
Linux 3.13
KDE 4.13
Intel core i7-4700 @ 2.4 GHz
Sphere with 1920 vertices -> 56 fps (memory = 3,854,916 KB) Note: Instant loading - file size = 165 KB
Sphere with 32720 vertices -> 55 fps (memory = 3,860,028 KB) Note: Instant loading - file size = 2.7 MB
Sphere with 122880 vertices -> 57 fps (memory = 3,945,024 KB) Note: Instant loading - file size = 11.1 MB
Sphere with 491520 vertices -> 41 fps (memory = 4,256,856 KB) Note: about ten seconds for loading - file size = 45.7 MB
Sphere with 1966080 vertices -> 18 fps (memory = 5,826,128 KB) Note: several tens of seconds for loading - file size = 187.9 MB
I understand that the system working at the limit, as the presents interruptions especially during the change the image magnification (FOV).
From these tests, and other tests that I did, I have the impression that the maximum number of vertices that can be used with a modern graphics card (4.6 GB Video RAM) is 120,000 to 200,000, with no great delays (.ac file size: 7-15 MB)