I felt that I should post somewhat of a follow-up to what I wrote regarding this lens sometime ago. I returned the "copy" I had written about, and finally got around to shooting a bunch with its replacement this weekend (after I adjusted it slightly with reikan focal). In short, the lens is quite good throughout the focal range wide open; and at f/4 through f/8 or so it's excellent. The bad news is despite what many see "on paper" this lens really isn't that much better (at f/4 and beyond, obviously) than the 24-105, except in the corners where it trounces it. That being said, the TS-E 24mm f/3.5L II is what I'd grab if I absolutely needed perfection at 24mm. But I digress. The 24-70 II definably also handles chromatic aberrations better than almost anything else I've ever used, and it focuses very very quickly. Problem is, I feel this lens is still way overpriced (yeah, I too paid for it)..
So, where I'm at.. I'm a sucker for both fast glass and for image stabilization, so I'm still torn as to which to lose. Chances are I'll sell the 24-105, but I'll be pissed that I shelled out so much for the new guy. Meanwhile, here's a snap from today... very good for wide open and brightly back-lit.. (50mm, 1/100th, ISO200). Cheers.