So, IIRC DMX runs at about 44hz if you've got a full dimmer pack (which isn't hard with moving lights since they each take a bunch of channels). That means you get about 20ms to compute each cycle, which strikes me as pretty soft indeed if you're running on PC hardware... I wouldn't worry about performance until you see problems.

Eons ago, I remember building a DMX controller by ripping out the clock from a standard RS485 card and soldering in a new (8khz?) one from Radio Shack so the baud rate would be right...