The 225/70R19.5 tires are about 32" tall, so the diameter may not be that far off from your 17's. I needed the wheel capacity for the payload I carry and previously drove a F250 running 245/70R19.5 tires.
I have put over 13K miles on the 5500 in less than 16 months just with camping trips. I think I will have sufficient mileage on the tires before they age out to justify the cost per mile. I was only getting 30-35K on the OEM Continentals before replacement and my 19.5's barely showed wear after the same amount of miles on the F250.