Is it normal for the burst rate to slow down when you stop down the aperture?

Did you actually observe your aperture as I recommended? It’ll be an eye-opener. At many exposure combinations the lens will remain stopped down or partially stopped down (in Servo AF mode). The ISO and E/V of the scene will also affect this. If you watch, you’ll see that the aperture will remain (wide) open at other times.

I’d presume that this behavior is to facilitate AF (and maybe other functions?)

I did check, and it behaves like I though it would (opening up all the way between shots during burst mode). I even set the aperture to the smallest it can go. I tested it in bright environments and dark environments and the behavior is mostly the same.

Maybe try resetting your camera back to Factory Default (always a good starting point).

I haven't tried resetting. I was hoping that someone with similar canon cameras would test theirs out to see if the same thing happens lol.

True. As to why your framerate is slowed in One Shot AF mode, perhaps the lens is partly to blame. Check lens firmware?

Everything is up to date.

I don’t recall a slowed framerate when I had my M5. I always had all in-camera processing disabled though. Check all of your settings.

I might try that. Even things like chromatic aberration correction and periphery illumination correct?

Since you mention that your Canon lens exhibits largely the same issue, it has to be something common to both (as you’ve been speculating). Have you tested this in different environments? You aren’t using flash by chance? (The M5’s responsiveness is slowed greatly).

I tested it in both light and dark environments, and the amount that it slows down seems unrelated to the light levels and ISO. No flash.

Thanks for your input.