Looks like you got pretty much all the factors considered... I've only used the 24-105 and not the 24-70 so can't compare them directly myself. I did like the 24-105 though.
On IS or not, generally IS will get you more of a benefit in low light than just one stop of aperture. It should be noted IS only helps against camera shake from causing blur. If the subject is moving, the longer shutter will increase the chance of that showing motion blur, so a bigger aperture may be more useful in that situation. As a further consideration, obviously the aperture affects the DoF you have at the time.
On IS and panning, depending on the IS generation, the IS may work differently if you want to use stabilisation while panning the camera/lens. Older ones don't support it at all, so need to be turned off while panning. Some have a dedicated switch for the stabilisation mode, either off, one axis, or both axis. For example, in one axis mode, when panning horizontally it will only stabilise vertical movement. Some implementations will detect panning automatically and set itself to do that without needing the user. I'm not sure which version the 25-105 has.
On IS or not, generally IS will get you more of a benefit in low light than just one stop of aperture. It should be noted IS only helps against camera shake from causing blur. If the subject is moving, the longer shutter will increase the chance of that showing motion blur, so a bigger aperture may be more useful in that situation. As a further consideration, obviously the aperture affects the DoF you have at the time.
On IS and panning, depending on the IS generation, the IS may work differently if you want to use stabilisation while panning the camera/lens. Older ones don't support it at all, so need to be turned off while panning. Some have a dedicated switch for the stabilisation mode, either off, one axis, or both axis. For example, in one axis mode, when panning horizontally it will only stabilise vertical movement. Some implementations will detect panning automatically and set itself to do that without needing the user. I'm not sure which version the 25-105 has.
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