Long story short - the XCD 135+1.7x on the X2D makes a perfectly lovely and sharp image when it is focused correctly. That means either that AF has done its job, or the photog has done it manually. Unfortunately, the AF will look for any opportunity to choose what you don't want. I *could* not get it to focus on a duck. Why? Ducks sitting still in still water. One blur after another. It's a mystery. (Insert HAL saying "these things have come up in the past, and they've always been attributable to Human error.")
The Zeiss 250/5.6 SA is - I'm not sure it's less sharp, but it has less contrast. To get the same "look", you have to add back some bite, and then the image is noisier. We're talking twigs 1,000 feet away. As mentioned earlier, manual focus is easier.
But the important statistic - the keeper tally heavily favored the Zeiss. If I could get better at manual focus with the XCD lens, it would have been much closer.
First some 250/5.6
Lamp stuck on.
Tight crop to show off focus. It was a bit of a production to switch lenses, so I don't have a lot of images taken with both - only distant air-distorted buildings.
Reflection of Fifth Avenue with Ducks!
And, of course, Soup
And from the XCD 135+1.7x