Portable Air Conditioners: Is amperage a better measure of cooling power than BTUs?
Some manufacturers will use outputs based on what we used to call "lab standards", which meant that the figures could only be achieved in a perfect setting or perfectly controlled environment.  With these units the testing parameters were controlled perfectly to obtain numbers that were not attainable in normal operating environments. Others use average numbers. If the numbers look to good to be true they probably are. As fixer1234 stated the difference could be a higher efficiency model, but in that case the price difference would be much higher. Sometimes the numbers are just too good to be true.----  And as for being able to get the room to 61 degrees, it is impossible for me to say since at some point as the temperature goes lower the A/C unit will just ice up and stop performing. These units are not made to operate at that temperature.