I am 6'2" and the 550 is just fine. But you should find one nearby and ask the owner if you can lay down in it. Maybe give them a heads-up before you come and tell them you will wear clean clothes and clean socks....
Also, the foot room is fine for me, and I have size 13 shoes (but I don't have any "topper" on the mattress). Even when you are flat on your back, your feet do not stick up vertically/at 90 degrees. Your feet are at an angle (45 degrees). So I doubt your feet would be a problem (except if you have a thick mattress-topper).
Also, no one really sleeps as long as their height - meaning, when you sleep, even on your back, your legs are angled from your body, so your feet are not really 75 inches from your head when you sleep. You don't actually need 75 inches from the top of your head to the bottom of the mattress, though I still think you should find a 550 and lay down. I would be very surprised if it's not long enough for you.
That said, there are other reasons to choose a 560 over a 550, though we are happy with our 550. If I frequently camped someplace where it rained during camping season, I might have wanted a camper with more inside space. But here in California, that's not too much of an issue.
I do agree that the SUV height is very important for a tall person. I prefer the higher countertop height in the kitchen. I'd like it even higher! (but I also have lower back issues, so...)
-Al