Late to the thread, but a few points:
1) Boo to people describing Roger's data as conjured or impossible to achieve. +1 to anyone who backs Roger, who is an absolute nerd/enthusiast who very transparently shared his perspective, methods, etc. This guy is a friend to photogs. Further, being at LR gives him the chance to test 5, 10 of the same lens at once, which many 'experts' on line do not do. My trust factor with his data is therefore very, very high.
2) To the 'it can't be better than a prime' folks, you are correct in principle, but throw the latest tech, design and (as an engineer, I'm assuming) spectacularly tight tolerances at the problem, and yes, a zoom can beat a prime. It just happened.
- To that end, in theory with that same level of tech/design/tolerance we should see *even sharper* primes down the road. As I am moving from zooms to primes, I find this attractive, though daunting for what the price might be.
- As a side comment, that same thinking has seen Canon recently produce non-L lenses that rival or beat their L counterparts. The new 24mm IS and (especially) 28mm IS lenses are right up there -- again, just with sharpness -- as the L glass of similar length. They aren't weather-sealed, or produce the same bokeh, but the sharpness is there.
3) Sharpness is great, but it isn't everything. We also need to consider AF, carrying weight, size in the bag, the color this thing produces, the new hood size (refreshingly smaller despite reversing the telescoping), the #$!# decision to go to 82mm filters (though I'm sure that's part of the math to get the sharpness we want), etc. The user experience should be about more than just sharpness, or we'd all be carrying howitzers around as our walkarounds.
In all, I expected Canon to pants the Mk I as it's 10 years old. I was not, however, expecting it to be this
I'm not drinking any Kool Aid here -- it's unbelievably pricey and we as consumers need to weigh purchasing decisions carefully. But on a core metric of sharpness, kudos to Canon. Now make me a super small wide L lens, dammit!