Put it like this. Whatever problems you normally have will be multiplied come winter season.
Especially with trying to match the bore size of the barrels and paint. Paintballs are a lot more fragile in winter and some of those cheaper paintballs aren't quite round. In the summer the shell will give somewhat, but in the winter its made even more fragile from the cold temperatures. We had loads of problems last winter, to the point of 3-4 paintballs completely blocking up a barrel.
I guess some of the newer J&J barrels could have been narrowed slightly, ie a smaller bore from the .688..maybe 685...but due to the conditions you all may as well just over bore with 691 693, which will at least stop the paint from breaking....
People sometimes over-bore in humid conditions as well, like playing PB in Florida. As the day goes on the paintballs swell (absorbing water) and hence are more prone to breaking in the barrel due to the increase in size, even when a bore/paint match was made at the start of play.
D.