A few months ago I broke my PL100-400 when I fell getting out of a boat on a muddy river bank. So I've been investigating the options myself recently. There are a few advantages to the Olympus 100-400 that I hadn't previously realized. The Olympus teleconverters are cheaper and more readily available (the Panasonic 1.4x seems to be only available used at the moment). Also, a comparison review indicates that the image at minimum focusing distance on the Olympus lens is noticeably larger than with the Panasonic/Leica – so that's a plus for shooting bugs and other macro-type subjects if you're into that (and I use my 100-400 lens for that a lot).When I was shopping for my kit, I also fretted over a fractions of a kilo between the Pana and Oly 100-400 zooms. In the end I went with the Oly lens to mate with Oly body. Yes, it is heavier, but guess what, I don't think about the slight difference in weight anymore. It's just about getting the best photos with my gear, and appreciating what it can deliver.