I'll be getting my copy tomorrow. I'll be pitting it against a Panasonic/Leica 100-400 I'm trying out. I just want to see if the Oly is either sharper, faster to focus track OR if it's image stabilization plays more nice with my OM-1 body. I'll let you know.
So here's my quick follow up. Got my Olympus 100-400 today. Against the Panasonic/Leica 100-400 it has the following:
* Faster to lock focus
* More accurate Focus
* Sharper image at ALL focal lengths
* The zoom ring is much more refined, smooth and accurate
* The controls have a solid distinct "click" when in position as opposed to the mushy one's on the Panasonic.
* In absurdly hot weather (atmospherics) it does a better job producing a sharp image, the Panny is fussy about it's temperature shot in.
* Sure, the Oly is a tad heavier but a much more solid build overall. The Arca Swiss tripod mount is another professional touch the Panny lacks.
This Oly may not have a PRO designation but it deserves it more than many.
I had the Panasonic 100-400 and was quite disappointed after trying mutiple copies. I think a lot of people put up with it because it was the longest m43 lens at the time.
I preordered the Olympus 100-400 and have not been disappointed one bit. It also doesn't have the problems the Panasonic had (based on my experience and a lot of online reports).