Dcrosby, You may be right at the edge of zone 5/6. Check the map here. If you are still zone 5, you just need to do some winter protection. It should be fine. Climate affects disease susceptibility. In dryer, more arid climate like AZ or CA, they don't have to deal with fungal disease like we do here in humid East Coast. When you read people's recommendations, you want to see where they live. Different climate gives different results to the same rose variety. Spraying for roses every week or every two weeks is not my kind of fun (anymore). I didn't even want to smell the blooms after I sprayed the bushes. Now I don't spray, most of my roses esp. Austins look naked by mid summer. Here is a link that might be useful: MA new plant hardiness zone map

i used to live.near lafayette indiana. sweetbay grew fine, the saucer types did fine, all hybrids with acuminata parwntage did fine. selected cultivars of southern magnolia, m. grandiflora did olay to fine, depending on location...they definitely preferred to be out of the wind...obvious by the end of winter, but they leafed.out fine and behaved as though nothing was wrong (edith bogue, bracken's brown beauty) . and there are a host of other species that would do fine...but unless you choose dedicate a.substantial chunk of your life, fortune, and sanity to magnolia, hardly worth the effort. for what its worth...the medium pink and plae.pink hybrids.of saucer magnolia did fine...tje darker the color became, the more red, the poorer it wintered. just an observation based on what i saw on the indiana prairie

30 years old PG could attain enormous proportions, something like this (20'x 20') but could be kept at any desired size as it's prunable. Lately I had a chance to inspect (closely) several of 10-15'+ PGs growing at old cemetery and all of them had one thing in common: thick scraggy unbranched trunk to 4-5' and then thinner, but still not productive branches that start producing live shoots only at 6-7' height off the ground. Due to droopy nature of PG, everything above 3-4' was green and flowering (from the distance), but I'm affraid that in a winter and spring it will be not a sight to admire. So, my point is, that since you'll be looking at your tree not from a long distance, but rather closely, you might be better off to grow it as a shrub rather than a tree. Just in case you'd like to see a 'Kuyshu', here it is trained to a tree. It's about 5-6 years old (2 years in my garden and another 3-4 years were trained to tree form by grower) and about 7' tall. As you could see it's much more upright than PG. I think most of 'full size' paniculatas could reach your desired size, but when choosing among them I'd avoid Tardiva as it is a latest to leaf out and bloom of all of them and in your zone you'll not see flowers probably till end of August, while Kuyshu start blooming in late July.

Ask this question on the New England forum also. Your part of MA has winter moths that can defoliate some kinds of trees more than others. There are a number of folks from zone 5 MA who visit the New England forum regularly and will chip in. I'd include a question about winter moth and other pest susceptibility in your post. There aren't winter moths in my area so I can't help with them, but I know that cherry trees around here are susceptible to a wide variety of pests and tend to be short-lived. There was a similar question there recently that might give you some ideas even though her size range started smaller than yours. You might want to consider whether you will want a mix of trees which will give you a longer period of interest and some protection from losing your entire shelter belt if there are disease or insect issues vs. having a more uniform look to your row of trees. You are making a good choice not to look at callery pears. They don't do well with the wet snows that often happen in New England. This is from last fall's Thanksgiving storm and the homeowner had to remove about half of 6 trees.