Hello Tim, I agree with Ralph about 5x7 and 8x10 in relation to a 4x5 Sinar F1 (or F2) rear standard. Format changing sets, 4x5, 5x7, 8x10 seems to belong to the P cameras (P1 and P2). The F cameras, at least the F2, seem to come in separate rear standards. I have myself a F2 5x7 rear standard and it is something VERY different from my 4x5 F2 rear standard, not just different frames as for the P types (though there is a special P1 and P2 rear bearer for the 8x10 frame, and a special, longer, front bearer to fit the 8x10 rear back; but you can use the standard bearer to 8x10 and 5x7 rear frames and bellows but not with the same movements as with these for 8x10 special bearers). My F2 5x7 rear standard is a very nice solid but quite heavy piece (built like a tank as someone said), not to compare to my nice light F2 4x5 rear standard. On eBay at least I have seen some F2 8x10 cameras, and I suppose the rear standard of these cameras are very big things, not just a big frame (bigger bearer than my F2 5x7 bearer, I don't know). For outdoor works these bigger F cameras are perhaps more stable than the P types, since the F types don't rely on the self locking system of the P types, but this is just a guess based on my quite old P1 special rear bearer.
Bertil