Thanks for the reply .
Well i cancelled the build on my level because it was taking well to long for me to keep going. I decided to put together a smaller test level with lots of cylinders and a wall covering in between.
Building with full light and visibility makes a HUGE difference. It appears that compiling one or the other does not seem to work at all for performance enhancements. Looks like the BSP culling only works if you do a full build.
Maybe i will test more tomorrow