Reality Factory

I plan to make big urban outdoor levels for my game, so I just want to know which will give better fps for my game --- the normal BSP level that are made in RFEditPro using the brushes or a city crafted in modeling program and then put inside my level as a Static Mesh. I just want to know this because RFEditPro is good for small levels but things seem to go out of my control for big levels.

I personally would model it externally. I forget which is better for frame rate though. You would want to split the city into multiple models and use LODs too.