It would be really nice if manufacturers supplied data. So many conflicting reports! I find, as a general trend, that when I use a zoom I'm cranked up to the maximum focal length anyway. Certanly not always, but most of the time. Also, I'm usually on a tripod, or at least braced, with the subject mostly sedentary. [This is very different from Donald, I would imagine...] That 400mm/f4 DO lens mentioned in one of the articles above is very exciting. Would not really need IS for my purposes. [Too bad it costs as much as a trip to New Zealand!] Short. Light weight. The best lens for the job often depends on other issues than optical quality. Just wish manufacturers would be more forthcoming about optical performance. [The pictures in one of the reviews above sure lool like the 200mm IS + teleconverter works pretty well!]