To call f11 a fast aperture is a bit strange - it is 3 full stops slower than an f4 lens, that is it lets in only 1/8th as much light for a given exposure as an f4 lens. Or 1/16th the amount of an f 2.8 lens at the same shutter speed.
An f11 lens is so slow that many folks thought Canon was joking when it was introduced.
That said, it seems to be a very useful tool within its limitations. I really wonder how well it will do for birds in flight after sun down - like chasing short ear owls, shot up to 20 minutes or more after sunset. A stop of two of light then will be really critical for AF and shutter speed.
I am really impressed just how well the images of the baby baboon in the deep shade look. Speaks highly of the R5 sensor and the f11 lens
I will probably buy either the 800 or the 600 despite the aperture. Small enough, and light enough, and cheap enough, and sharp enough to be very useful in better light.
I really do wish Canon would deliver an f4 600mm DO lens - now that would be something to crow about.
@Vilen Can't you find a Sigma or a Tamron 150-600 style zoom for a Sony body mount or use an adapter for your Sony body? I found this Sigma 100-400 F4.5-6.3 GD DN lens in this review