I'm thinking about getting a longer lens for my RB67. The current longest lens I have is the 180 f4.5 . I'm debating on the 250 or the 360 - Will there be enough difference between the 180 and 250 to be worthwhile? My uses for the long lens would be picking out details, either architectural or landscape, and full length as well as close up portraiture, mostly in the environment but maybe in the studio. For the studio, I've got the 180 which I think is plenty long enough. Opinions? Also, which version(s) are best? Is there enough of a difference optically between the original, the C, and the K/L to justify the difference in price?