Opticallimits has released their review of the RF 24-70:
Canon RF 24-70mm f/2.8 USM L IS - Review / Test Report
www.opticallimits.com
I have a few remarks to the review about some statements that differ from my own experience. I guess parts of it can be explained by copy to copy variance.
First the vignetting. I can confirm that there is considerable vignetting, but please be aware that it is even and smooth. I don't find it disturbing. That said, in general I don't mind vignetting, so take that into account.
When it comes to sharpness, the results Opticallimits presents does not match my own experience. My copy of the RF 24-70 seems to be at its best at 35mm, while the copy Opticallimits has tested seems better at 50mm. This is either due to copy to copy variance, or it can be that my examination is done at infinity focus, and opticallimits measure at close distances.
With regards to bokeh balls, and the quite busy inner "onion-like" inner structure displayed in the review, I would like to report that from my very limited experience with the RF 24-70, I have only seen smooth bokeh balls. My only examples is with a f2.8 aperture. If this "issue" bothers you with the opticallimits review, I recommend looking further into it, and that you don't take the review pictures for granted.
One thing that made me very reluctant to invest in the RF 24-70, was that it, from what I could figure out from TDP, didn't seem to be much difference IQ wise, compared to the RF 24-105 L IS. This impression can be backed up in the review. Opticallimits states that:
On the more affordable side is the Canon RF 24-105mm f/4 USM L IS (right). For the vast number of photographers, it is actually the more sensible choice. Yes, it is a stop slower but it has, obviously, a range advantage and while the difference in price may give us the impression that it is optically inferior, this is not the case.
This statement about optical performance does not correspond with my own experience. I have now compared the RF 24-70 to the RF 24-105 at infinity focus at 24, 35, 50 and 70mm, at f4 and f8. While the 24-105 is a strong performer, it is poorer at every focal length and aperture than the RF 24-70. The 24-70 is sharper, has better contrast and better clarity. In parts of the frame the 24-105 gets a bit hazy, with poor contrast and clarity.
Every zoom has some variation in its performance. What I see though, is that at the edges where the RF 24-70 at certain focal lengths is slightly worse than I would like to see, it is still as good as the RF 24-105 is at its best edge performance. When the whole frame is considered, the RF 24-70 is significantly better.
I would say that if you are on a budget, you should definitely go for the 24-105. It is really good, but it isn't as good as the RF 24-70, at least not at infinity focus.
My honest opinion is that the RF 24-70 has proven to be a better performer than I expected. It doesn't have any serious weak points, and stopping down solves the few issues that I have with it.