Which model NeoAir? There are NeoAirs, and then there are NeoAirs. The regular models are intended for summer use, and have minimal insulation.
In a nutshell:
X-Lite: lowest weights, R3.2
X-Therm: heavier than X-Lite, R5.7
All Season: slightly heavier than X-Therm, R4.9
Trekker: Heaviest of all, R2
The shape is also something to consider. The two X-series are severely tapered and rounded at the shoulder. I found it hard to use them without an arm or leg hanging off somewhere (not what you want when it's cold.) The All-Season and Trekker are rectangular, and I never had anything hanging off.
Since my days with the NeoAir, I've switched to the Q-Core series from Big Agnes. I never liked the BA Air Core or Insulated Air Core pads, but after nearly a year with the Q-Cores, I have to say I really like them. They're in the same weight and R-ratings ranges as the NeoAir All-Season, and I find them a bit more comfortable. They have a slightly raised edge that is very effective at keeping everything on the pad.
If I needed a higher R-rating than the Q-Core, the Exped Downmat 7 would be my choice. I borrowed one once in really cold weather with snow on the ground; it's a tad heavy, but well worth lugging around for the extra warmth.