Upload & Sell: Off
What is the difference between the two?
About 1.5 lbs, 2 stops of IS, and, based on what I can tell, a non-trivial increase in sharpness, especially with the 1.4x.
Allens is awesome. I got my 500 MKI there and whenever I finally decide between the 500 II and 600 II will get my lens from him again.