+2 on the pad.

A plain air pad with no insulation will get cold in the 40's F. The air inside gets chilled from the ground and the air, and conducts heat away from your body. Every time you move, you stir up the air in the pad, bringing more cold air in contact with your body. Even for an Insulated Air Core, freezing (32*F) is close to borderline. By the time you get into the 20's F, you need a pad with R5 insulation, or a closed-cell foam pad placed on top of the Insulated Air Core pad.

I went through this a couple of years ago trying to use a NeoAir at 18* temps. When I laid still long enough to find out, I was plenty warm on the top and shivering on the side next to the NeoAir!