(Note* Polygons are trigonal)
Visuals: 35,000 polygons per map
Collisions: Single, solid mesh, unlimited (but shouldnt ever go over something like 3,000ish)
ELU: Limited amount of textures can be used for ELUs (I think it is 16?), and 5,000 polygons
Full Scene: Something like 45,000-50,000 is the maximum polygon count. (excluding npcs, weapons, and players)
For information on texture limits visit my guide here:
http://forum.ragezone.com/f497/wucas-texture-sizing-dds-894668/
Remember: Density also matters, although you have the capabilities to go somewhat crazy, placing 2,000 polygons in a tree leaves will crash you; I know from personal experience.