Q. Does DX Studio use any kind of optimization algorithm for the levels,
like BSP trees, Octrees or whatever? Does it have any tool for creating
portals (or turning a 3DS mesh into a portal or occluder)?

A. DX Studio throws most data straight at the card, which is now becoming
faster than BSP given it's quicker for graphics hardware to blit it than
it is to test for inclusion. It does also support LOD which helps slim down
high poly models as they get further away.