Okay, having received the new iPad (are we calling it the iPad 5?) I checked out the Belkin Ultimate for iPad Air and the Zagg Slim Book, also for iPad Air. By Air I mean 1st gen as that is supposed to be the same dimensions as the iPad 5. Now, that may be true, but the Belkin's attached case that is supposed to fit the back of the iPad did not fit at all, it was too narrow in depth. The depth of Air and 5 is 7.5mm I believe but the Belking felt more like Air 2's 6.9mm. I tried hard to get it in but all I did was nearly break it (that is not a euphemism, BTW).
The Zagg Slim Book on the other hand fits perfectly. The slight issue for me is the concept of the case back, with the iPad in it, is attached to the keyboard by a pair of holes in the plastic case and magnets. Admittedly the magnets appear to be strong and I don't feel it is not secure, but still...
The other issue with the Zagg keyboard case is that the holes for the volume buttons do not quite line up right and the dividing bit of plastic of the two holes actually pressed onto the up volume button. I solved that by cutting the plastic away with a craft knife and sanding down. Obviously the Zagg has a little weight to it, so together it feels a bit more like my old iPad 2 and Logitech ultra thin keyboard case but I can live with that. Overall I am happy - smiley face.