For what it's worth, I had both the 24-70 and 24-105.
Using the 24-70 with my 60D and 580 EX ii on it at an (ex-) family wedding, it just got to be too heavy for this 64 year old body. A similarly long, indoor, standing-only event I shot 2 weeks later with my 24-105 instead of the 24-70 came out just as good, in my estimation, and not the weight. I sold the 24-70 as a result of those two events. Canon claims the IS is a couple of stops. So, other than f2.8 bokeh on the 24-70, I didn't lose a thing. When I want bokeh, I mount the 135 f2 L.
I've gone to all L glass with the exception of my 85mm in the expectation I'll be moving from the 60D to full frame soon...like next years' tax refund. If you have any similar plans, you may want to rethink getting any EF-S lenses that can only be mounted on crop bodies.