In my experience, bikes with upright riding postures, like the NC700X and the CB500X, are much better on the back. Even though I don't have a bad back, just looking at the 600 Shadow makes my back hurt because of the forward foot peg position on that bike.
I'm 5'8" with 32" inseam and I can flat foot the NC with boots on. The CB500X is even easier to reach the ground. Inseam is a more important number that overall height.
You can always add handlebar risers to get the bars farther back and put you in a more upright position and help your back. You can also lower the bike's suspension a little if short legs are an issue.
I own and ride NC700s because I like the engine, but I do think the CB500X is more comfortable. The reach to the bars is closer on the 500, and the stock seat is more comfortable.
No offense, but my memory of riding experiences in rural New York was that the roads are quite rough. Getting your foot position more underneath you, as opposed to a cruiser position, and also maybe improving the suspension, should make it easier on the back.