Some of you will be shocked to find out that I have put Bow Brand gut strings in my third octave, up to and including the C string, but not the D and E, which are still nylon. Apart from having lousier harmonics that require more work, I now have a truly seamless transition from gut to nylon. The strings are a bit thin, but are pretty close in clarity to the nylon strings.
And, the Burgundy strings I used in the fourth octave were just fine, no problems with them at all.