I'm not a big fan of trying to design a level that runs ok in SW mode, in fact, I don't do it. I know it's kind of selfish becuase everyone doesn't have decent hardware somtimes. The problem is, it starts to limit your creativity. I mean think about it. We already have to curtail our design becuase of limitations in the game engine.
I'm just waiting for the day when we port the crazed ideas from our heads directly over to a game that can handle it, I'm sure there would be some great levels.