Ok, so a follow up for ppl who are not familiar with the Bougs. After seeing the growth on Jan 21st, I waited a couple days and decided that "if" I was going to do root work on these plants, I had better try and do it as they were coming out of dormancy. (The other option was wait until spring, with the possibility of setting them back through May/June)
So, the smaller of the two took the rootwork quite well, lost a few bracts and leaves, then bounced right back afterwards. The larger one (about 3" or 8 cm at the base) didn't like the work that I did on it at all. However, this work was much more invasive as I tried to cut thick old roots from the vine, and leave all or most of the newer roots intact. It appeared to me that this plant is about 15 years old, but had been removed from the ground possibly 1-3 years ago. It has some good root growth much of the way around the base. In one particular area where I removed a large section of old root(s), it exposed an area of new roots directly above it, and as the root came free the new roots drooped and all of the soil fell off.
As I have mentioned before, I suspected that the roots themselves aren't that delicate, but the contact point between the roots and the base of the vine are the weak spot. "In my mind anyway" I think I have proven this point, because the plant went straight into dormancy afterward (or near death), and is now beginning to show signs of recovery. However, of the 4 branches that come from the trunk, I suspect that I have lost one of these... will know for sure in another month.
So, if I was going to characterize the Bougs reaction to transplanting, I say that they are as tolerant as most plants, if all you are going to do is rake out the roots and put it in the next pot size up. They are going to be troublesome if you intend to reduce an old root system to fit in a bonsai pot. And they are going to be highly problematic, and possibly die, if you mess with the roots a lot, and allow the new roots to flop around (flexing at the root-to-base contact point) more than absolutely necessary.
To reduce the vibration on the plant itself, I used a 4" cordless angle grinder with a masonry disc to cut, and a 60 grit flapper disc to clean up the cut afterwards. (For me, this system works the best on all of the "larger" trees... basically anything larger than you could properly use root pruners on.)
Of course, this has only been my limited experience with transplanting these vines, so take what I say with a grain of salt... my intention is to share what I've experienced, because there is so little information on them as a "house plant in zone 3"...