The new level I started on is barely started. I built and textured one set of stairs in Max. The mesh is going to be used 6 times in one room. After setting the first stair and testing the map showed about 90 or so FPS. I said well thats very acceptable. I duplicated the stair 5 times. Tested the map and found the FPS had dropped to 40 (still in the green) but can't be acceptable because of there will be more meshes in the same room which could cause it to go down even more.
An anti portal is a brush that can be placed inside a mesh that will block tris so to speak. I placed one anti portal in a stair about one grid from the floor. Not touching anything bsp. When I tested the map this time the FPS was at 100 or better from anywhere in the room. So once again you better monitor the stats of the gameplay as you build or the FPS could get out of control really fast and become unfixable. Be sure to check out UDN's page on Level Optimization. Also another thing that needs to be watched is compile times. The old level seemed to compile fast to me as I was used to the long SDK compiling times. The person that had looked at it for me said it was taking way too much time to compile. This was due to the bad building on my part. Build it good and the compile should be extremely short.

antiportal: sounds like an excellent tool but, the name doesn't quite seem fitting based on what you say here.

Yes I know. Anti. I think they are supposed to work kind of like the hint brush that don't work in SOF2. Lots of info out there for portals.