I think you would be crazy to buy the 70-300mm DO lens. The 70-300mm f/4-5.6 IS (non-DO) has excellent optics and probably outperforms it in IQ. I haven't touched the DO lens so I cannot compare build and feel. The non-DO version is very light and portable.
If you are going to be spending that kinda money on a lens, why in the world wouldn't you get a 70-200 f/4L IS or a 70-200 f/2.8L?????

