Wish you had answered my question but it's all right. I agree with the others, the space blanket won't be THAT much help. Before I got a sock I sometimes used one by laying it in the hammock, putting my sleeping bag in there, and wrapping it over the top to create a little half-assed sock effect. Blocked some wind, maybe captured and reflected a little heat I don't know. I really didn't consider this a major component in my sleep system though.
When backpacking I normally use a 15 degree Eureka Casper synthetic insulated bag. At 6'-3' around 240 lbs I'm a big guy but not so big as you. With that sleeping bag I can go to 38F with no problems, no supplemental bottom insulation necessary. Some will say this is impossible, don't know what to tell you except my THEORY is, the lack of compressibility that "down fans" decry in synthetic bags actually works FOR the bag in this case. Also I'm a fairly "warm sleeper". I don't think this would work as well with a down 15 bag, but I don't have one so I can't say for sure.
Same bag will take me a little below 30 in comfort with just a torso-sized CCF pad. If it got anywhere near the 15 degree rating of the bag, yeah I'd freeze my ass off. Actually this is true even if I was using my UQ, the Casper just isn't that true to it's rating.
Anyways, while I do LOVE my UQ (and would probably love a down UQ that much more), CCF pads are probably the best "bang for the buck" and right in there for "bang for the weight", so don't dismiss them out of hand.