I'm loving the 100-300 f/2.8, and I use it a lot with the 1.4 TC attached. It has a long enough reach for owls, but of course it's inadequate for smaller birds. I'll be using it as my main lens for photographing bears on a trip this summer, and I probably won't even need the converter for that. But if I do, I'll still have the wide end covered with the 70-200 f/2.8 on a second body. The 100-300 is easy to hand-hold, which is a big plus. I don't own the 2x TC and I'm pretty sure I never will. The lens really shined on my trip to Brazil last year, where I was photographing wildlife in very dim light. The f/2.8 aperture saved the day (see below). All in all I'm very happy with it! But if/when the mythical 200-500 f/4 comes out, I'll sure be tempted