I also suspect that swamp cooler cfms are inflated, as fans used to be. Air King's 9166 whole house fan is listed as 8908 cfm in Grainger's 394 catalog, but Air King says it only delivers 3560 under the current test method, which measures the actual cfm flowing through the fan, without adding the room air entrained by that airstream after it leaves the fan.
Most of the swamp coolers in Grainger's catalog are now listed with an "industry standard rating" ("a numerical rating for comparing similar models and sizing purposes") instead of "CFM." For instance, their chart says a 5NV70 WisperCool model RW5000 cooler with an "industry standard rating" of 5000 can cool a 1200 ft^2 house in Las Vegas.
Moving lots of air wastes water and electricity. A Las Vegas homeowner might do better with Sam's portable 797895 Arctic Breeze cooler mounted inside a house near an open low window and an exhaust fan in a higher window with a one-way plastic film damper. Turn on the cooler when the house temp reaches 80 F and turn on the exhaust fan when the RH reaches 60% to keep the house air at the upper right corner (80 F and w = 0.012) of the ASHRAE 55-2004 comfort zone.
A 1200 ft^2 house with R30 walls and R40 ceiling and 96 ft^2 of R3 windows and 0.2 ACH (I suppose nobody builds houses like that in Las Vegas) would have a thermal conductance of 1200ft^2/R30 for the ceiling + 96/2 for the windows + 1024/30 for the walls + 0.2x1200x8/60 for air leaks, totaling 128 Btu/h-F. July looks like the worst-case month for cooling, when it's 91.1 F over an average day, with an average low and high of 76.2 and 105.9 and humidity ratio w = 0.0066 pounds of water per pound of dry air.
Keeping that house 80 F while evaporating P lb/h of water into C cfm of outdoor air means 1000P = (91.1-80)(128+C). P = 60C(0.075)(0.012-0.0066) = 0.0243C makes C = 108 cfm and P = 2.62 lb/h, ie 7.6 gallons per day. If the house has significant thermal mass (eg a floorslab), we can save more water and energy by only running the cooler at night.
Why do we need 5000 cfm???