my new tablet locates gps signals very quickly but I'm not cycling with that!
Theoretically, just for the sake of argument, you could make a tablet sturdy enough for a tour by putting it into a Griffin Survivor case, but then it becomes an inch bigger all round and an inch thick, and weighs about the same as an Abus Granit X U-lock, around three pounds. As Colin Chapman didn't say but should have, "You can have small, fragile and very expensive or thick, big, expensive and sturdy, choose only one combo."
My iPhone cost more than my iPad anyway, if it is a consideration of cost, but the iPhone is so much more convenient on the bike, it is no contest. I have a Griffin Survivor for my iPhone too, but it is not in use since the iPhone is in a Mophiejuice battery case, too big to fit the Survivor. I love the Survivor and if I were to tour extensively, I'd forego the Mophiejuice and in favour of the protection, and charge the iPhone off the main battery for the bike. The iPhone screen is big enough to read maps, but the picture quality in any kind of daylight is pretty frustrating. Ditto for the excellent built-in camera.
BTW, another tip about stuff you need to download to local in-phone memory before you leave home, if you don't want to run up roaming bandwidth charges, is your reading matter kept in Dropbox. Once you leave your LAN (your computer's wifi umbrella, basically the block on which you live) anything that appears to sit in Dropbox that you haven't opened in another application, isn't actually there until you connect to the net again. A pain, that.