Chris
For what you are looking for I would stay away from the American DJ side and look more at the Antari stuff. Not saying ADJ stuff is bad but you will get a lot more output from something like the Ice 101 which is their low lying fog machine, and something like the S-200 which has more snow output and I beleive you can run it for a longer time. On the Mr.Kool it would take around 4 or 5 times to cover that area and its about 3 mins in between each shot. On the Snow Flurry you can run that until the fluid goes out of it, because there is no heater on it you don't have to worry about any down time