Hi Alan
So I am not a scientist
and I don't have enough hands to operate a stopwatch for the exercise.
About the cards, with a Sandisk Extreme Pro 300 Mb/sec SDXC II card of 32GB capacity, at shutter speed 1/1250 at f4.0, iso from 400-640, with Release and Speed priority AF enabled, I can get 29 RAW shots before the camera stops. With that card, it seems that within one second or perhaps one and a half seconds I am able to start shooting again, not the full 29 but at least some bursts of 4 or 5 frames.
With the Sandisk Extreme Pro 95 Mb/sec SDXC I card of 64GB capacity, at shutter speed 1/1250 at f4.0, iso 400-640, same camera settings for AF as above, I can get 28 or 29 RAW shots before the camera stops. With this slower card, it seems that I can start to shoot again within about 1.5 seconds roughly, but its two or three shot bursts before it stops again. The main benefits with the SDXC II cardseem to be in if you fill the buffer then delay before you can start to shoot again is significantly less.
The third test I did was to use the SDXC II card (300 Mb/sec) again, but with the camera set as above except image quality was changed to C-RAW, and the 90D took 113 shots before filling the buffer. So a viable option for action sequences...
Cheers
Grant