I was an NBC NCO in the military. The masks we use are mainly for particulates. They don't stop fumes, which is probably the most dangerous part of painting. Your mask will probably take the spray out of the air for you, but it should clog the filter(s) pretty quickly.
Your best, and cheapest, bet for spray painting is an inexpensive, throw-away particulate mask. (You can get 12 packs from 3-M for a few dollars.) DON'T WORK IN A CONFINED SPACE WITH JUST A PARTICULATE MASK. You'll either get high, or dead eventually. Best solution is a filtered, pressurized suit, or at least the helmet.
Trust me. A pressurized helmet is not overkill. Check some local paint shops.
