Well, decision made (sort of).
My local camera store had one (yes!)...so I decided to grab it. I also decided to hold onto the 70-300 for now since I could not decide what to do yet.
First impressions - never had the old version so can't compare to that....that said, tried it out on my 5D3...finally, a true telephoto I can use with that camera! Even with the crappy lighting in my apartment forcing ISO 6400, images still looked quite clear and sharp. Definitely a winner and money well spent
I can say this - this is one of those "shoot with confidence" lenses - seems to be consistently strong throughout the range, even all the way open at 4.5-5.6. But for $2K you'd expect nothing less...
The "zoom throw" or whatever you call it - it's very long. Getting from 100 to 400 quickly requires a long twist of the zoom, so for those who want to go quickly between the range, perhaps the push/pull of the old version is better for that. But - at least it doesn't pump dust nearly as much (and precise framing is much easier).
There is a tightness ring that allows you to adjust the resistance of the zoom mechanism. You can also lock it at any focal length. I notice a bit of "zoom creep" phenomenon on my copy when I have it set all the way to loose (in fact, if I point it directly downward, it will "self-zoom" from 100 almost all the way out...) - don't know if anyone else's is like that.
Also - f/4.5 doesn't last for long at all. By 135mm you're already at f/5 (the 70-300 doesn't reach f/5 until about 150ish IIRC)...but you don't hit f/5.6 until after 300mm...so this lens DOES have a 1/3 stop advantage at 300mm over the 70-300
. As a bonus, it performs just as well at that setting, so you don't have to worry about any quality difference. Where the 70-300 does win out is on size and weight - there is a CONSIDERABLE difference in handling between the two lenses which should be noted.
I have not tried it on the 7D2 yet...but with the weather outside and the lighting in here, though, it'd be useless anyway.
ETA: also...it seems as if the lens is not truly 400mm when focusing on close subjects? Seems to get a bit shorter...