here is the conclusion: I like the lens...a lot
... me, too, and I bought it back when it had a reputation as being an overpriced version of Canon's non-L lens - but it's interesting to see how it gained much more recognition since then. I esp. like the still handholdable weight for ext. periods of time and walking around vs. the 70-200Lii (ymmv).
Just a some random additions to your again very nice review:
* The 70-300L's white paint is just for show, there aren't lens elements that would heat protection like in the 70-200L. One drawback of the extending design is that you cannot camouflage and protect the lens completely with a neoprene hood.
* I really doubt Canon will add f8 af for the 6d and wouldn't advise anyone to gamble on that. On my 60d the Kenko likes to hunt on low contrast objects when using single point af, and for multi-point the 9 af points usually is spread too far apart - so while 6d/5d3 might do fine, on crop it's rather for static objects.
* Close up performance is nice when not wanting to change lenses (I took some surprisingly good butterfly shots with it), but it in no way reaches the performance of the 100L macro lens. Another issue with the 70-300L is that it is missing the focus limiting switch of the 70-200L and 100L (thanks, Canon!), so if the af misses it takes a lot of time.
* The IS on the 70-300L is really good (at least 2ev) and the lock is instant and nearly not noticeable - but there's a catch since it still needs a little time to be most effective. So for quick point & shoot it's nice to have a stable viewfinder and being able to set the af precisely, but in my experience waiting for a second is a good idea.