Another thought came to mind about indoor or "enclosed spaces" performance enhancing. I usually only include four walls for the viewing frustrum, but if I'm walking around in tight bounded spaces, then it could prove useful to go ahead and at least add the far end frustrum wall.

This frustrum wall can then in turn be adjustable. So when you're walking around the room the outer frustrum wall will then become the bound of the outer wall of the room you are facing, or if you are in view of a corner of a room (where multiple walls meet), just keep the frustrum along the previous wall you were viewing (unless that place intersects with the room at some point).

This is just another thought to throw out there (I don't see a lot of activity run through this forum, so I figured I'd keep some discussion available every so often)

Also, can someone explain why on earth you'd use a "near" plane in a viewing frustrum? I have failed to see it's use since the four other planes (left right up down) converge and automatically cut things behind the viewer. The near plane would just create this little awkward clip space right in front of the viewer not allowing one to fully "approach" an object...