I have a very similar setup to you, D800+ into a Super Twin everything set to noon most of the time (vol & gain). I also own Super Compact and I would say you could get by okay with a single 12 if you have it raised up off the floor. The single 12 isn't gonna feel or sound as big as the 2x12 but it should be loud enough. This is assuming you're running off your cab alone.
If you always have PA support then just get the smallest cab you can find and run it tilted back in front of you like a monitor (I used to do this with an original midget back when I did the whole covers thing).
Thanks for this. Much appreciated. Do you run the D800 with the same volume and gain settings when using the SC? I`d be a bit concerned that if I do need to just nudge the volume up a bit from noon, that I run the risk of damaging the smaller cab. I should note that 99.9% of all gigs I do is without PA support.