I've been waiting on this lens. I currently shot on the long end with a minolta 500 f8 reflex. It can be fantastic in broad daylight, but that's a crippling factor most of the time. I'm not surprised to hear about the optics being a mild improvement over the former. In fact, they've talked up the SSM motor upgrade more than anything. If it was a major leap in optical quality you'd be hearing about it from Sony. The biggest problem with the current 400mm is the weird Bokeh at 400mm and drop in sharpness. Here's the skinny:
No AF with a teleconverter- anyone looking to nail birds all day long with this will definitely be using a 1.4 along with the lens. Makes that SSM worthless at that point.
70-200 IMO is worthless on a lens at this price point. Your just not using that length all that often.
I want this for ease of use. But, I think I'm still going to eye up a minolta 300 2.8. And thats the problem, I only care about the 300-400 range on this. It needs to be compared to the minolta 300 2.8 or the 200 2.8 which has already been proven to be sharper with a 1.4 tele than the 70-400 at 400mm.