I would suggest investigating what are known as "ironclad rhodies". This is a listing developed by Ernest Wilson at the turn of the last century of rhododendrons (mostly catawbiense hybrids) that were able to withstand long term plantings at the Arnoldia Arboretum, so able to endure some very cold temps. This listing has been expanded for modern times with some newer cultivars, including the many PJM clones.

The leaf size will be variable depending on the parentage. But just an FYI....smaller leafed evergreen plants tend to be more cold tolerant than those with larger, broader leaves.

Ironclad rhododendrons

Thanks for this, will have a look now.!

The “Marjatta” series of hybrid large-leaved Rhododendrons were bred in Finland with claimed hardiness down to Zone 4 (but definitely solid in z5). More info can be found here: https://hortnews.extension.iastate.edu/2000/3-24-2000/selectrhod.html

Additionally, many of the R. catawbiense cultivars (“Album”, “English Roseum”, ”Grandiflorum”, “Roseum Elegans”) and their hybrid descendants (“Nova Zembla“ and many others) will give you both the large leaves and excellent cold hardiness. You’ll probably find many on the list of Ironclads that GG already provided.

I like using this search engine from Rhododendron.org. It lets you put in multiple parameters such as size, flower color, and hardiness, and you want to choose elepidote in the last line which just means the big leafed ones. (Lepidope Rhodies have smaller leaves like PJM or even smaller.)

http://www.rhododendron.org/search_multi.htm