Lensrentals.com has completed a teardown of the brand new Canon EF 70-200mm f/2.8L IS III and compares it to the Canon EF 70-200mm f/2.8L IS II. They discovered that there really isn't any difference between the two in how they're built.
From Lensrentals.com
Well, as Canon stated, there is no difference between the Mk II and Mk III versions. If you think there’s an optical or performance difference, please contact me about some Tennessee Beach-front property I have for sale. If you’re in the market for one of these in the near future, I’d snap up a Canon 70-200mm f/2.8 IS II at discount price if you can find it.
If you really like the new color do what we do for touchup paint: take the tripod ring from your friend’s Mk III to your local paint store and have them color match some enamel for you. Canon claims the new fluorine coating makes it easier to wipe off oil and smudges. I think the new fluorine coating is easier to wipe off. Could be Canon and I are both right, could be just Canon is right. Read the full article
Rent the Canon EF 70-200mm f/2.8L IS III USM at Lensrentals.com
In addition, this may explain why the one and only time my MkII dropped about 2ft on to a dirt road (in a soft case) that I thought I had broken it. But once I bumped it a few times, it was fixed. I suspected it was the IS mechanism that got stuck due to the shock. I guess I was right. And very lucky! Now I guess I'll start locking that lens!
I wonder, companies like Sigma and Tamron can take their single optical formula and launch it with different mount for 3-4 manufacturers. Could Canon just delay this wonderful release and instead of Mk. III announce it as 70-200 with RF mount by keeping the same optical formula?