I really don't see a need to question Dustin Abbott's integrity on lens testing. I would argue that large magazines and websites that make their money through advertising by big camera companies, or click-throughs to stores have more to gain by biased reviews.
I think *all* reviews should be questioned, not so much because of intentional bias, but because of testing variations, and as mentioned by previous posters, variation between copies, esp. w/big glasss. when the lens is out, we should have 5 or more reviews to look at, and unless there's some conspiracy, we should get a consensus on qualities based on bench tests.
My only concern is how will this lens work for me. That's not just theoretical, it's practical. For example, I do not use a tripod, I shoot either handheld or with a monopod. So even if I had a sharpest lens ever made, I would introduce some shake which would affect results. I value a fast and effective stabilization system and that's my biggest hope for this lens. I'm sure it will have to be stopped down at least one full stop for optimum optical sharpness, and that it will *not* be sharpest at 600mm. So, the question is...how will this work for me at 400-500mm compared to a more expensive 100-400 L? or the Bigma??? I think we'll all find out soon and that will end the some of the speculation.
Good points, and one of the biggest reasons why Roger's conclusions are LensRentals are so valuable. He has access to more copies than any reviewer I know, and I trust his assessment on the technical end. My reviews are more about real world use, and are much less useful scientifically and hopefully a little more useful for those looking for practical application.