Both good points gents. Either way, I think I'm going to default to the 5 gallon setup and see how it rolls, the 3 gallon kegs will work (I'm thinking hang a bungie cord from the ceiling above the cooler, from a screw in hook that I can take anywhere, then adjust the tension until the keg is at the proper serving height.)
I've got a local restaurant selling me as many 5 gallon corny's as I want for smoking price, and I just found the Igloo for $44 via my BNA Amazon link shopping, so I'm bout to pull the trigger. My jigsaw has been sitting in the shed for too long.
Thanks for the measurement BP.