I have a gap between my 70-200VR lens and my 500mm f/4 AF-S II lens. I am considering the 300mm f/2.8 VR and the 200-400 f/4 VR. Here is my rationale for leaning toward the 300mm lens. f/2.8 vs. f/4 6.3 lbs. vs. 7.2 with a 1.4x teleconverter, I'll have 420mm @ f/4 the D2x crop mode will give me a little flexibility considering the 300mm is a fixed focal length vs. the 200-400 range. at 7.2 lbs., the 200-400 is just too much of a beast (same size as 500mm) to hand hold. Do I have this right? What do you think? Thanks in advance.