That's the real question. The diference between this and its oder model is
1) It's got a UD lens element
2) Second IS
mode for Panning.
3) Circular Aperture (I don't know if the other one was different, this I am writing from the Canon Catalog I got)
4) 70mm instaed of 75mm at the lower end.
Advantage over F/4 L is
allowing shot without blur at 1/60secs at 300mm and also panning.
Ofcourse Quality is not to be "L" level, but wait to see some actual pics from Anetters.
The question is whether Picture and quality is closer to 75-300mm IS
(old model) or the 70-200F/4L.