Or, you could RAISE the maximum viewable distance, but that would increase r_speeds.
Incorrect. Polygons beyond the maximum viewable distance are being rendered. They're just not visible.
Although there is a certain compile parameter for Zoners tools that implements distance into the visibility determination... I've never experimented with it though.
As for your map, ZeG, you should fix the leak instead of creating a skybox. I assume you know the disadvantages of the skybox method?