good thread, we should continue this, when we speak of replacing the fan with a bigger one and worry about less air moving we should remember that even a couple 1200rpm slipstreams would be worlds quieter than some(/most?) projectors, you could for example make a soundproof zigzag soundproofed (foam etc) wind tunnel cooling the projector with acousticpack inside and all around the front upto the lense so all noise projects

backwards away from the listening position reduced to near inaudible even with 4 120mm 1200rpm fans (undervolted to desired air/noise ratio) and keep your projector cooler than with the standard screamer fan
(cooler = longer bulb life?)
i have a vent in my room (basically a square hole in the wall with a plastic grill screwed either side) which i plan to duct to the projector with something like (and probably borrowed from) the one out the back of my tumble dryer

with a 120mm (hopefully undervolted) 1900rpm slipstream at the vents end (quieter but may not be sufficient, may have to be at projector's end) which would pump very cold air into and through the projector hopefully increasing the life of the bulb and dramatically decreasing the level of noise