I just played a cold weather game last weekend and both my V2 guns (M4/MP5) were fubbared! Cracked the mechbox on the M4 as well as broke the hopup.
Monday, picked up a TM AK Spetsnaz which has the V3 box which also proved to be a workhorse in the cold. All the people with V3's were shoot full auto with no concern.
In warmer weather I will be going back to my M4 as primary as it's a beast but I now will be rebuilding the box so it's on the shelf for now.