A reminder that UE2 quality terrain is possible in UE1
Realistic terrain + Demo map with funky domed skybox (and 3DS MAX converters)www.silveribex.com/mt/archives/000043.html
Zoning the map could help performance.
You can use large sheets and divide the map based on the terrain, or put zone boxes around the various groups of buildings or other areas with lots of stuff.
Zoning buildings can be a pain if you put individual sheets in doorways and windows, but you can just put 1 cube in the walls of the building which will often use less sheets (depends on how many openings).
Each zone can have different overrides such as body counts and distance of rendering certain effects.
Stacked maps should be their own zones also (or just sealed normally which will zone them). This can help reduce the sound travel and confusion caused by hearing a fight above or below.A note on audio ambience
For this sort of game type and weaponry, I would very much recommend using the new audio renderer from OldUnreal and adding EFXZone info to the map, or individual zones if added, so that a natural outdoor reverb and distance of sound can be set (obviously buildings or structures, even woodland/forest can have more suitable reverb preset).
The newer audio system is ray-traced and uses occlusion, so bounces off surfaces and is blocked my meshes such as a breakable window or movable door.
If you are in a building, gunfire outside will sound like it is outside. Likewise if you are outside and people are having a firefight inside, it will sound muffled and contained.
...unless they are inside a hangar perhaps, in which case there is also a hangar preset
It should be noted that Smiftsch has made it so that if the map is loaded by someone using an old audio renderer, it will just ignore the extra info and still work, so compatibility is not a problem.