When testing the Altis map, I create a single rifleman as player and a single quadbike. Loading in, I get about a minute of 30FPS to 40FPS, then the performance degrades badly, to between 0FPS and 8FPS. Graphical glitches happen, my soldier disappears and after a couple of moments, the level of detail of items in the viewport goes to what appears to be absolute minimum.
Occasionally, it can be rescued by using the LSHIFT+NUMPAD- "flush" command, but generally this has no effect.
On other occasions it can be rescued by changing the textures from high to standard, but if it works, it can only be done once. Another occasional rescue operation is to change the display from fullscreen to fullscreen windowed. {F21750} {F21751} {F21752} {F21753}