Being worth an upgrade from an R3 is pretty specific and personal. If there is something you would like to know, I am happy to give it a go.
The R1 is a phenomenal camera. But like every other high end camera, there are a lot of individual parts that add up to the overall sum. A few points:
- EVF is bright and large. Much better than the R5s which is really good to begin with. You may not notice if you just pick one camera up, but I have recently been switching between cameras and it is very noticeable.
- The resolution difference is not what people want it to be. I am not having a problem resolving details of small birds 10-14 meters away with the R1. I am still working on comparative images but the few I have done remind me back when Nikon came out with the D800 back in 2012. 36 MP and people were talking about everything having to be perfect to take advantage of all that resolution: great lens, perfectly still/tripod, faster shutter speeds, etc. While I know a lot has changed working with the R1 and trying to compare it to the R5 is reminding me of those discussions. It is difficult to take advantage of all that resolution. The smallest things will throw you off. In short, I am finding the 24 MP in the R1 to be very good.
- Buffer. Haven't hit it, but I've posted the best buffer comparison I have seen is posted in the R1 thread.
- AF is great. Not perfect. Do not believe the "game changing" language. But it is better than the R5, which was already very good.
- Control over fps in ES is great. I am set for 7 fps, 12.5 fps and 30 fps.
- AF-on/Smart controller is great. I really like this and do like the dual levels.
I could go on. Let me know if there is something specific you are interested in.
Regarding the R3,
Bryan's rundown is the best I've seen. Overall, I do get the sense that you should only upgrade from the R3 if you are looking for something specific that the R1 offers. It seems to have been concluded that the R3 has slightly better DR. But nothing that would really be noticeable unless you are specifically doing a side by side test, as
Jared Polin did here. But then the R1 does have some advantages. While I have not seen a good comparison, theoretically, the R1 should have better AF. The buffer is better. And being able to customize the AF-On/Smart Controller and jump from one set of FPS to another FPS is great.