24-70/F4 IS vs 24-105/F4 IS

What exactly (apart from the FL) is the big difference here? I can imagine the 24-70 being a bit better optically but is it really that big a difference? Just wondering since I recently got a FF with 24-105 and love this lens.

Less distortion, sharper, slightly better IS (an extra stop I believe), macro.

All in all, not worth the new price for me. I'd much rather get the Tamron to get 2.8 for the price of the Canon 24-70 f4 IS, but since I want this to be a walk around lens, I wanted more range than 70mm on the long end, and went with the 24-105 with which I am perfectly happy.

Haven't been able to use the 24-105 much but after a few hours, I'm liking it at least as much as my 17-55 (now sold). Which is saying a lot since I almost wanted to marry that lens

As Sirrith said, the 24-70 4 is a bit better. When buying a new lens, that 'bit' may be a consideration. If you already own the 24-105, I don't think the 24-70 4 offers anything worth upgrading for. I'd love the 24-70 2.8 II, but the price is too high.