"If you find the Neo Air that warm, then I would not be surprised that you find the Symat warm to 20F. My point is that there is not a 0.6 R-value difference between the two pads. I would not be surprised if it is closer to 1.5R in comparison testing."
I happened across this older thread because I was researching the Synmat UL (which looks awesome....might get one - mostly to try vertical baffles and the wider outer tubes). Kinda fun to look back on these comments in light of the State of the Market article now out.
Depending on the level of inflation, the Synmat tested at R 2.7-3.8 (R 3.25 average) while the NeoAir tested at R 1.6 - 6.1 (R 3.85 average). We can see that at an average level of inflation, both mats are warmer than claimed, with the NeoAir being warmer than the Synmat UL. Perhaps David had the NeoAir under inflated, as that really drops the R-value. The NeoAir R-value does vary with inflation level quite a bit, which might actually be a good thing because you can top it off for cold nights, or let air out when it's warm.