At Building Panoramics we have both lenses. I can assure you the new 24-70 f4 is significantly better than the 24-105. Too early to tell on the IS yet.
Is it worth the hefty price ? If you can afford it then yes. If not, don't loose any sleep over it !
I've just posted a pic in 'best landscapes' shot on the 24-70. You can see a much bigger version on our website.
Sporgon, I highly respect your work, so you comment carries a great deal of weight. Do you find the 24-70 f4 sharper than the 24-105 or is the IQ better in other ways? Do you have any side-by-side shots with the 24-105 and 24-70 you would be willing to share?
@bholliman: many thanks for that.
Despite the reviews that are floating around about the 24-70 f4 saying otherwise, this lens is sharper than the 24-105 across the focal lengths. For instance at f5.6 - f8 it is equal to the 40mm STM and 50mm 1.4 at those same focal lengths in centre and mid frame. It is not as good as those primes in the corners. At 24 to 28mm it has less barrel distortion than the 24-105 as well as being better across the frame. The 24-35mm range is much better spaced. Some reviews have stated that 50mm is the lenses weakest focal length: this is not what we have found. Colour rendition, contrast, chromatic aberration etc similar to 24-105. We have found no issues with rsa in the way we use the lens.
The 24-105 on the other hand is not as sharp as those prime lenses mentioned above. It is also worse in the corners at the wider focal lengths.
However we are in the digital age, and computers generate the pictures we produce. The resolution of the 24-105 is of sufficient quality to allow very effective sharpening. People are quite rightly raving about the quality of the 40mm STM. Apply an un-sharp mask of say 0.2 pixel @120% and a good copy of the 24-105 will produce an image that is pretty much the same as that lens. This is why we use one at Building Panoramics, and will continue to do so for the foreseeable future. Most of the pictures that we currently have on our website are shot with one or other 24-105mm lenses.
At present the 24-70 f4 is in the south of England, and the other's in the north, but when we have the two lenses in the same place I'll produce some 'real life' back to back comparisons.