I don't disagree with Nate's suggestion that you rent.


However, it *sounds* like much more concerned with reach than with MFD or IS. You've tried 280mm and know you would like more reach than that. This being the case, the 400mm f/5.6 seems the way to go.


(Sure, you could put the TC on a 300mm in a pinch, but if you're primarily going to want the longer focal length, get the longer lens).