Money and weight no object I'd agree but the 24-70 is a huge chunk of glass and a big wedge of cash when compared to the 24-105mm!
It's a great travel lens for general photography on full frame, it hardly left my camera in Iceland last week and when it did that was usually to attach the 14mm for Northern Lights shots. It is sharper than most lenses and renders a nice image it's not the greatest for people shots if you want back ground separation but that's the compromise of the size and weight. The IS is really useful for taking hand held landscapes and scenery shots and can cover for a flawed technique, cold hands or a strong breeze all of which I suffered from!
I wouldn't touch a 24-105mm F4L on a crop body I'd opt for either a 17-50mm f2.8 or if I wanted more length and width a 15-85mm.
Don't get me wrong I'd have a 24-70mm f2.8 if I could justify the cost but I have found the extra width, length and IS a real bonus coming from a Tamron 28-75mm f2.8 and I didn't miss the stop of light too often.
yeah, on FF it starts to make more sense; the focal length is much nicer, you are a stop faster anyway and have the shallower DoF and you get a lens more like a 17-65mm f/2.8 on crop. But then that is just the point, why pay for a FF body and then use a lens that you would easily get equivalence to on a crop camera and get identical results? I would rather have a Nikon D7100 with a 17-55mm f/2.8 than a D800 with a 24-105mm f/4.0 (24-120mm in Nikon land) and have money left over for more lenses with.
The 24-70mm f/2.8 is really where its at on FF for wide-normal zooms. To get the equivalence on a crop camera you would need a 16-45mm f/1.8 lens which traditionally would be impossible to get... until Sigma released the 18-35mm f/2.8!
yeah, the 24-105 is smaller and lighter then the 24-70mm f/2.8, but the 24-70 is not exactly big or heavy. And if weight and size is an issue then you shouldn't be using a FF DSLR at all, go get a nice mirror-less setup
I'm with Raymond on this one, the 24-105 and Nikon 24-120mm f/4. are really glorified kit lens that kind of sit in a no mans lands of inbetweenness. The Nikon is marginally more temping because 120mm starts to become noticeable above 70mm but not really. What would temp me was if the lens was a 24-200mm f/4.0 or a 18-75mm f/4.0 or 20-140mm f/4.0 etc. Either give me more reach, go wider or a bit of both while maintaining f/4.0, then you have a cracking GP lens but 24-105 just doesn't given anything above the 24-70 to justify loosing a stop and accepting reduced IQ, IMO.
But horses for courses, if it works for you that is great, I just don't see it work for me. I also see too many people taken in by the marketing that FF bodies, L glass, red/gold rings, nano coatings suddenly gives you magic abilities and instantly turns you pro. L glass in particular is really misunderstood, it mostly just refers to build quality and price rather than anything particularly relevant to an amateur photographer like image quality, aperture, etc.