So, regarding the XT being the best keyboard IBM ever made, I must concede that I may have spoken too soon. While I do consider the XT to be the best of the traditionally available Models F floating around, I just tried an F107. It turns out these are better.
The keyfeel and build quality of the XT put it above the 122 and AT, in addition to the keyboards derived from it, like the Bigfoot and so on, but the F107
feels like an XT, but weighs as much as the sun, and also you can use it with a virtually modern layout. Indeed, the layout may be the best of the Fs, because you can use Windows and Context Menu keys, unlike even a Model M.
Unfortunately it means you might have to buy a bigger desk.