No, I don't use ent_preload.

But I think this could work with the terrain, using level_load, or even converting to models and doing it that way, maybe with ent_create. Then the program can remove sectors not needed and re-add them when required. It would take a little longer to load all of the world this way, but that's also true of other games of this scale. Initial loading takes longer than your average fps, but the game "flows" without any problem.