@roseseek testing to see if I can @ someone who's not commented yet.

There's a pattern with trees and shrubs in general where the edge of hardiness for many kinds is USDA 6 with 5 being the start of slipping into the realm of winter cold being significantly limiting. Consistent with this:

Would Zone 6b [be] an appropriate bound[a]ry or can it [ANNE BELOVICH ('RUPannbel')] grow in cooler areas?

In general Wichurana hybrids do fine in zone 6 and even zone 5 most winters with some dieback expected

https://www.helpmefind.com/rose/l.php?l=2.63265.2&tab=32

@Mischievous Magpie (CO 5b) yes, it worked! It didn't alert me via email but the bell icon beside the "Your Houzz" icon at the top right of the screen contains the notice. Had I not looked there out of curiosity, who knows if I would have noticed it? Jeff Stover from the RHA grows it in his Zone 5b garden per HMF. How successfully, I don't know. I've never grown it in anything "harsher" than 9b. If it helps, the lineage is (Wichurana X Floradora) X (Pinocchio X China Doll). Have any of these been successful where you are?

@roseseek Truly I don't know the answer to that question. I'm not super knowledgeable about many types of roses, the only wichurana I can even think of seeing around here is the hybrid, Dr. Huey lol. Though that rose is bulletproof here it seems, growing sometimes to 8x8 and never a hint of dieback or disease on it.

'Dr. Huey' tends to have mosaic in my part of USDA 8. And this occurrence is not limited to my area. With of course many plantings of it here tracing back to installations of grafted combinations produced in other parts of the country and shipped here. Combinations wherein the modern hybrid scion froze in a sharp winter (apparently = any temperatures much below 10 or 15 degrees F. for very many hybrid teas and the like) or failed for other reasons. Leaving the 'Dr. Huey' to continue on without it.