I'd have to say that I'm somewhere in between with my POE Max Thermo. I'm not really comfortable below mid-30's. In the other thread Mark started about sleeping pad warmth/weight ratios (http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/6336/index.html), he has the Big Agnes Air Core (comparable to the Max Thermo) at a higher R value than 1 inch self-inflaters like the Prolite, but I'm much warmer on the self inflaters (I use a POE Max Lite 1.0 3/4 length, discontinued) than on my Max Thermo. To confuse me more, I consider myself a warm sleeper!
Anyway Ryan, if you supplement your Max Thermo with a closed cell foam pad (and you probably won't need much, I use a torso length 1/2 thick piece similar to the Z-Rest), use it on top, where you'll get the insulating benefits of the CCF pad next to your body. These pads work by trapping your body heat in the pad. If you put it under the inflatable mat, there's not much heat making it all the way through the POE pad to the CCF pad below and it won't help much. I've done this successfully in temps well down into the teens.