"I'm sure there are air pads with 30D fabric and 900 fp down that performs just as well or better. Actually, I know there are, but I don't care to search BPL for those at this time."
Actually it seems the Xtherm wins as being warmer for the weight than down, although a complete apples to apples comparison is hard to find data on.
Options I could find:
1) NeoAir XTherm = 15oz, R-5.9, 72" x 20" x 2.5" with rounded corners, 30D fabrics
2) Kookabay DAM with R-6, 72" x 20" x 2.5" with TAPERED cut, 70D fabrics = 18.2oz
3) Kookabay DAM with R-6, 72" x 24" with TAPERED cut, 30D fabrics = 16.97oz
The option #3 Kookabay pad is very close spec-wise to the Xterm (30D nylon, 72" long, same R-value, same thickness). The main difference is that it's 24" wide, but that's at the widest point and it's got a heavily tapered shape (see pic @ link). It tapers to about 12" at both ends, so from the looks of it, there is a very similar amount of pad present here. Assuming they have the same area (big assumption) then the DAM is 2oz heavier than the Xtherm.
Option #2 definitely has far less total pad area, as it's a 72" x 20" x 2.5" with a tapered cut that shaves off a lot more area than the rounded corners of the Xtherm. Yet the total weigh is 3.2oz higher at 18.2oz. This pad does use significantly heavier 70D fabrics, so the question is whether that would drop the pads weight to quite a bit less than the Xtherms 15oz, because this pad is clearly narrower (on average due to its tapered cut). This pad would probably have to weigh about 13oz to be just as warm for the weight as the Xtherm, since it appears to have 10-20% less surface area. Could 30D fabrics shave this much weigh (~5oz)? Maybe, but IMO the best case scenario for DAMs is that they equal the performance of the Xtherm. Apples to apples is hard to do, but it seems the Xtherm weighs the same or a bit less as a 30D DAM.