I did this in class today, I sketched out a map in Photoshop, then for the hell of it, exported in grayscale, and made a height map out of it. To see what it would look like, I applied a texture, exported, and put it in BSP. Surprisingly, it worked, the results are below, but the framerates seemed too good on the school computers... I assume epoly I counts entity polies, i.e. func_model, and it never climbed above 1k (I'm sure I could reduce it by making a better model). My question to you Q2 mapping gods, is this a bad practice, assuming I could make the terrains texture look great? Bear in mind, I'd only use this practice where clipping/fixed viewpoints make since.
Cheers,
y00tz