Canon has obviously put a lot of R&D time and investment into the R5. This project must go back 5 years (at least). I spent my life working in R&D in another high tech industry and will guess that the R5 is behind schedule, likely originally intended to launch with the L trio of zoom lenses. These kinds of major projects never go perfectly. Nevertheless it looks like its going to be a marvelous piece of engineering.
This forums and others seem to have narrowed down a key set of important questions:
1. Autofocus performance. The 1Dx3 feedback in mirrorless is quite positive. So the initial reviews of the R5 will be very interesting, esp the BIF tracking.
2. Stabilization performance. CR guy said a while ago he's seen a video of the R6 IBIS stabilization and that it's excellent. The announcement last week that EF lenses also benefit is a bonus. I assume the RF lenses will significantly outperform EF lenses in this regard.
3. EVF performance. Perhaps the 1Dx3 is a clue here. Presumably, the R5 EVF will perform similarly to the rear screen of the 1Dx3 in mirrorless mode. YouTube videos (e.g. Jared Polin's shooting women's NCAA basketball) look very smooth. What do others that own the 1Dx3 say about this?
4. Buffer capacity. This has been a major 'wow' item for many. In video it's particularly surprising that the camera can perform 8K on-the-fly compression to H.265, a processor intensive task. One possibility is that this will be quite limited due to heat generation (2 min?) but 8K video RAW recording can go until the CF Express card is full (at 80 GB/min for 10 bit 30p if I've calculated correctly). There's been some speculation that Canon is working with Samsung for their chips. This makes a lot of sense. Samsung has world class lithography capabilities and small, energy-sparing transistors will certainly be required for these data rates. Inferring again from 1Dx3, it looks likely that consecutive RAW stills for the R5 will be high capacity. The R5 will be moving roughly 1.7 times as much data as the 1Dx3 at full speed, but the latter seems to have nearly infinite capacity for consecutive RAWs.
5. Price. We should make no mistake that Canon intends to maximize their profitability with this camera. This is a once per decade(s) opportunity. They will use it as a lever to sell RF glass, so profit margin will benefit from both. When the 5D5 launched, for example, the EF glass was out there and buyers of the camera were only buying the camera. In the case of the R5, nearly every buyer will also be making RF lens purchases. The winning equation will be to keep camera price in check and thereby sell lots of profitable glass. The recent video from Canon USA confirms this IMO (yes, they directly refer to the 5D2, but they're dropping a very clear message with no face-saving way to back out).
My two cents. I will am considering buying an R5 and lenses immediately since I'm upgrading from 5d3 and am recently retired and chasing light a lot more often now. If the camera doesn't deliver, I'll switch to Sony. I think the odds heavily favor an R5 purchase, but time will tell.
