I live in NH which can also get pretty cold in the fall. If it's below 55°F the only ball adjustment that I'd make is switching from a ProV1x to the regular ProV1. I find the ProV1 to bit a bit softer than the ProV1x.

I'd be very hesitant to switch to any ball that has less green-side control to the ProVs.

Additionally if the cold is affecting your drives by 20 yards or so, that switches your approach shots from short irons to mid irons—and I would not want to loss any spin on these shots. With ProVs I'm still holding the greens with my mid iron shots. Also I doubt that an NXT is 20 yards longer in the cold—perhaps a few yards but not nearly enough to justify switching.

I switched from the Pro V1x to the NXT Tour S last winter for basically the same reason.  I did gain some distance back, but not 20 yards.  The NXT Tour S did check up fairly well on the greens and felt great when putting.  My recommendation...buy a sleeve and try them out to see for yourself how they perform in the colder weather.  By the way, I went back to the Pro V1x when the temps started to warm back up.