Neil, I agree the focus looks right where it should be on this last one. Ultimately it's difficult to answer a question regarding IQ with any lens if there aren't other shots to compare to from the same photographer. I say this is regards to the fact that nearly everyone seems to do some sort of PP, or in camera custom setting that sets their images apart from others. I'm guessing, at least, that birders with serious levels of equipment seldom post images in untouched fashion for presentation sake. Therefore it's hard to find such images for comparison online. I've seen some really dynamite images from other 400 4 DO lenses, where I would never think the dreaded "lack-of-contrast" issue even exists. But is that because of PP? Hard to say. I suppose if the detail info is there it may be the shooting conditions that are making the biggest difference.
That said, this last shot looks better than the first two, to my eyes. It looks as though it was taken in sunlight, so maybe a factor. If you had the time, would you be able to post a couple of 100% crops, both from a cloudy shot and a sunny shot? I'm not an expert, but sometimes the answers to the contrast can be seen better at the detail level.
You also mentioned being happier with shots on less dreary days. A couple of those to compare to might help.
). I may well think twice about recommending them again, down south anyway :-O.
