More high praise for the 24-70 II, with the usual caveat of price.
Question for people who've bought the 24-70 II and had/have the 24-105mm f/4L IS 'kit lens'. Did you keep the 24-105L, and if so, now that you have the 24-70/2.8 II, do you use the 24-105L any more?
I have a hunch you won't want the 24-105.
But, just to put a different perspective on it...I've decided that I'm most unlikely to replace my 24-105 with a 24-70 II. The 24-105 is a wonderful lens, even if the 24-70 II is better...and, to be honest, I only ever grab the 24-105 when I haven't a clue what I'll be shooting. And, when I don't have anything already planned out, whether the resulting shots are superlative or merely very good doesn't make a bit of difference to me.
Seems rather silly to me to blow that kind of money on a "whatthehell" kind of lens, at least as I'd use it.
If I did a lot of event photography, if I already used the 24-105 a lot, if any of the other common conditions applied, I'm sure I'd upgrade. But I don't, I don't, and they don't, so I won't.
One other thing I know...if I did
upgrade, I wouldn't keep the 24-105. It's probably just me, but I'd rely on a second lens to cover the missing length...either I'd already be doing events with a two-body setup with a 70-200, or I'd just pocket one of the short telephoto primes (with the new 100L being on the short list) and swap at leisure.
So, that's my advice. You use the 24-105 a lot, so it's very likely worth the upgrade. Those of us who don't get a lot of use out of a standard zoom, it's too much money for not enough extra.