Hi,
I thought worldcomp was created to solve this issue.
So if you split your map 3x5km or whatever size it is into managable tiled sizes then you increase the frame rate. Hide land being loaded/streamed in with fog.
This way you are dramatically reducing the amount of collision on screen at any one time. The more tiled map segments you have the faster you will get it to run. If you run into problems at 47,000 instances (I found 35,000 limit for 70fps) then ensure that over say 9 tiles you don’t exceed that amount. This is because the tile the players on is only one tile and you may also want the tiles round the player also to be visible. And obviously the player needs to see a tile to be able to walk onto the next one and so on and so on.
I used this technique in NO RETURN UDK version 0.135 if you want to test it in action. a 350sq-km map was made using the tiled/worldcomp setup and as you will find all the trees have collision.
I haven’t used worldcomp yet as I too was looking for an easier solution, but it looks like worldcomp is the only one provided in the editor just now. A player location based solution will probably be provided at some point I imagine.
http://www…com/games/no-return/downloads/no-return-v1135