None will grow 4 ft. wide and then stop growing, yet remain alive and attractive - you will have to prune. Different cultivars of Asian box vary in extent of winter bronzing, look for kinds that have better green color retention at independent garden centers.

I only grow Dwarf English Boxwood....Never have any discoloration or disease

'Suffruticosa' is the most susceptible familiar kind, scroll down for table.

http://ir4.rutgers.edu/Ornamental/SummaryReports/NJNLA_NJPlants_BoxwwodBlight_20140121.pdf

Indeed on BB. I was googling BB+Winter Hardy Boxwoods last night, and came across a Saunders read on BB hardi or less susceptible ones. Still researching as foliage and growing shape (rounded) vs. conical is where I'm at. Just wish the ones I tend to like (like GV, WG, and or GM) which are the ones that are more cold hardi AFAIK, grew a bit faster. I believe one that I have not see in person is sprinter