The faster HSM motor is a draw, but how does it compare to a USM lens
2.8->4 is one stop. Unless you are pushing the boundaries of what the camera/lens combo can do and absolutely need 2.8 to push the shutter speeds as far as you can to freeze action (and can't do that by pushing the ISO one stop further), the IS of the 24-105 will give you a far more useful 3ish stops of light. IMHO of course....but the extra stops hmmmm
Well now I'm plunged into indecision. Any downside to the Tokina, which I had never considered before?