I am considering (and at this point likely to) purchase a Canon 1GX II, sell my trusty 24-105, and buy a Canon 24-70 f/2.8 L II.
My thinking is: use the 1GX II for everyday/always have a camera with you stuff.
I presently use the 5D2 & 24-105 for that.
Upgrade to the 24-70 f/2.8L II.
I like to shoot wildlife and would then carry the 1GX II for unexpected wide shots, the 5D2 with 70-200/1.4x, and 1D4 with my 500 mounted.(Additional extenders handy.)
I am unsure whether the upgrade is worth it to me as the 24-105 is a good lens, although the 24-70 gets rave reviews.
The nice thing is I have time to think about it as the 1GX II won't be available for a month or so.
Also I am waiting to see what new FF bodies Canon brings out.



