That's just what I'm doing - levels without any BSP geometry, except a single block that is very small (8x8x8) with a sky texture to get skies to work. Blocks can't get as big as my levels are, but with other tricks I have, who really cares? Everything is based on using nothing but models because of their extreme rendering speed. I have a level that is almost entirely BSP and it barely manages to get 5 fps with the whole level in the view and that's with simple shapes and snap being used. My latest model-only level, in theory, with even 50 times the detail the BSP level can run in excess of 60 fps and that's without LOD implemented (using my much more flexible LOD system). It could be over 100 fps with LOD.

Others often refer to 3DS Max as "professional". There's Wings 3D, Blender, and Milkshape to name a few others. Still, you'll have to do a format conversion, of which I don't know much about.