Hallo Wayne, thanks for your PM, will try to expand my previous post.
I must start saying that I didn't have time so far to photograph with these lenses as much as I did with the 250mm in the past. However, in regard to the 180mm for portraiture, it's undoubtedly much more handy. With the 250mm, bellows extension really is an issue, and at times I had almost made my mind up in purchasing a small extension ring to help close focusing. Camera shake is troublesome as well: attempting a handheld photograph is quite out of question. As expected, the 180mm minimizes both issues, and especially in regard to close focusing it seems much more intended for portraiture than the 250mm. (as a side note there is a "soft" lens - 150mm I seem to recall - which is specific for portraiture, but that's very hard to find and IMHO too close to the normal focal length for being of any other use). It is as well somewhat shorter and lighter, and both things together with lesser bellows extension help balancing the weight of the camera-plus-lens block a lot.
I didn't seem to get your question about DOF very well. DOF depends only on aperture when subjects have the same linear dimension on the negative, not on focal length (excepting macrophotography, I mean). What were you exactly asking for?
About the 360mm, I believe that long focal lengths are extremely hard to judge because most (if not all) of the times weather conditions (fog or haze, or air turbulence due to heat) and various issues connected to camera shake consist in a severe limit to their performance. That may be why, so far, if I'd qualify the 180mm as an "outstanding" lens, I'd qualify the 360mm only as a "good" one. It would be very interesting to go out and photograph in a crystal-clear day and see how good it really is (but that happens very rarely in northern Italy) or to concentrate on close architecture details. It must be said, however, that such a long lens is a rarity in mid format's scenery, and perhaps worth having only because it has been made. It is "an opportunity", to use a word very familiar to people from the States.
About lenses' structure, the 180mm is a modified-Tessar type with asymmetric design, while the 360mm is a true "telephoto" lens (the 180mm being actually a "long focus", and the 250mm a weird way-in-between, perhaps a long focus with a field smoothener group toward the film). Because of its design, the 180mm has all the diaphragm/shutter blades unprotected outside the lenses (toward the film plane) which can be disturbing at first sight (they are indeed far recessed, and almost impossible to damage even with careless handling). It has as well a rounded square frame which acts as a sort of fixed secondary diaphragm and tends to get loosened with age, but is very easy to glue back in place.
Since I personally (repeat: PERSONALLY) like asymmetric lens' design a lot as it minimizes the number of air to glass surfaces and the number of lenses altogether, the 180mm scored another point in respect to the 250mm for me (same happend for the 127mm, which replaced my previous 90mm). However, this is mostly a distinction biased by the fact that I happen to be a boring physicist. Please disregard it, and choose your focal lengths in respect to the photographs you intend to make!
