Have to give poor Senior Prom a shout out. For decades it has been AARS rated 3.7, and honestly, while not an amazing rose (more because it is just a "decent hot pink" and no more), it certainly is not 3.7. Like most Brownell roses (as I think has been established) that Sub-Zero title is all marketing. The Brownell HT's are, in my experience 6a, no more and no less hardy than "most" HT's....people trying these now days generally get a less than strong plant (seems like 2nd tier garden centers/mail order catalogs) still list these and often nothing else, so the plant arrives not so strong and then everyone believes the never-ending hype and doesn't provide any protection. The plants die and the variety takes a hit. Note also that the Brownell's were from Rhode Island which is more temperate than say, Iowa, were Buck is said to have tested every seedling over 5a or 4b winters with no protection.............and yes, in my opinion, although they lack character to me the Buck HT's/GR's are quite hardy.............