Anything using blocks causes a big slow down. Blocks render very slowly. If using a big block, the effect is just as bad as several smaller ones. It makes little difference if using simple cubes or octagonal cylinders. As long as it's a block, it'll cause a big slow down. Blocks should only be used for indoor levels, although they can be for any setting. Blocks create portals to help speed things up, but for vast, ourdoor levels, portals have little or no effect. Plus, with a model-only level, the time needed to build the level is practically instantaneous. That whole city level shown in my screenshot, takes but a half second to build, probably not even that. The only slow down is WED - try loading a model with 60,000 faces once and time how long it takes to load. It can take at least a minute. The fix is to build the level up from scripting it and ent_creating the entire level.