To really answer this question, you would have to do a scientific experiment in which the temperature was the only variable. Lower the temperature but keep all other conditions the same, until one of the guns starts to consistently fail.
I can almost guarantee you, in order for the above experiment to produce credible results, the temperature would have to be lowered past any naturally occurring condition on Earth. I believe both guns would continue to function well below -50 F. I could be wrong, but that is my guess.
So, if my theory is correct, it doesn't matter unless you are taking the gun to Neptune. And if you are, I'd upgrade to something with a little more power, like a phaser from the armory of the starship you will be on.
Call me a caliber snob, but it is well known that someone shot with a phaser will fly 20 feet backwards and die instantly.