Sizing a window AC for bedroom, but with extenuating circumstances
I would go larger, I have installed many heating and cooling systems and when the systems are running properly the AC will cycle more often, icing is more of a problem with very high humidity and or low air flow and this can happen even in the desert on a hot day if the filters are dirty reducing the air flow while the system is working at its maximum cooling capacity.
I find customers are happier being able to turn the thermostat up a little verses when the room is still hot with the AC at its lowest setting running full blast. An over sized unit may cost a little more because it may cycle the compressor on and off more often but this cost will be a small percentage of the annual cost to run and you have a better chance of keeping the room comfortable.