Regular vs Arctic:
* Regular is just a single layer of fabric (vinyl?) so little to no insulating
- "Soft" plastic windows
- Windows on doors unzip, to open
* Arctic is insulated/pleated (the insulation kind of looks fiberglass like, but more dense).
- "Hard" plastic windows
- Windows do not open
The size of the windows are very different. In the doors, the regular top has a large window while the arctic one has much smaller window. (again doesn't open/unzip.). In the rear curtain, the window is wide on the regular top, while there are two small windows in the arctic top. They're positioned well for the driver to look back and see well, but the rear view mirror becomes useless, unlike the regular soft top.
The hard windows can crack if the screws that hold them in place are over torqued (which seems to be fairly common from the factory.)
With that said, I went from the 4-man regular soft-top, to a 2-man with arctic for the winter. I've not yet experienced a winter with the HMMWV yet, but it should help.
I'm currently driving around with the arctic top and rear curtain, with the regular doors, I'll switch the doors out in a few weeks when it gets colder.