"For those who already own the older 600mm lens the decision becomes slightly more clouded. The new lens does not bring any real world sharpness advantages over the older version. The decreased weight and minimum focus distance however may just be worth the cost of the upgrade."
Really??? Pay another 6K just for some weight and closer focus?
He really missed the boat on the reasons to upgrade such as improved image stabilization and all but highly desired increase in AF accuracy with newer bodies like the 5D3 and 1DX due to closed loop AF system....and even with that is it still worth spending 6K to upgrade from the 600 F4L IS? I could buy a couple more 5D3's or a 1DX with that 6K.
I don't think he missed the boat, at all. Sure, on test charts the 600 II is better. But the original was very sharp. The AF might be slightly more accurate with a new body - but the AF on the old superteles was already excellent.
There's no way I'd have considered buying a 600/4 MkI, even if it cost less than a 300 MkI. The original is too heavy to hike with, too heavy to handhold. I'd have bought the 500 I, even though it's really not long enough for me on FF. The reduced weight of the 600 II (as the reviewer aptly stated, it's a 600/4 lens in a 500/4 package) was the main
reason I bought the 600 II.