I love my R5, and would be looking to add a second body to my kit in time for a trip, preferably and R3 but possibly a second R5.I'm curious, and I hope some folks will reply. On all of these R3 threads of late, I see many users comment on how they already have an R5, but were hoping to get the R3. In some case, perhaps, to replace the R5, a camera that they bought only in the past year and costs almost $4000. I guess I don't understand why an R5 owner would want an R3. Is there something about the R5 that doesn't suit your needs that an R3 would? Is it the integrated grip? The more rugged build? Just the fact that you want the latest and greatest? Curious minds don't quite get it, especially for those looking for an MP count closer to the R5. Wouldn't the R3 just be a more expensive version of the camera you already own, with little or difference in actual functionality or results?
The R5 is really amazing in many ways. There are some areas where it is less great. For instance, the tracking can sometimes lose the subject (think erratically moving hummingbirds). Tracking is not as good in low light, and can get confused by busy backgrounds. I really hope that Canon releases some improvements to the R5, particularly the autofocus, via firmware, but so far we've not seen any stills-oriented firmware enhancements for the R5, so there is no way to know whether any of these AF improvements are coming.
If the AF and tracking from the R3 is more "sticky" and performs better in low light or with busy backgrounds, it will make a great complement to the R5 for the faster-moving subjects, possibly. I've noticed that the larger the subject is in the frame, the better the tracking works for the R5. Sometimes, this means that shooting in Crop mode yields better tracking results, when getting closer to a skittish subject is not possible. At 24MP, Crop mode would not be an option, which would make the R3 a less great second body for small wildlife.
I'm waiting to learn more about the R3 and the upcoming R5 firmware updates before making a final choice between the two for a second body.