BIF with R5 and RF 100-500mm compared to A9II and FE 200-600 G

Steve W wrote:

I'm currently using a Sony A9 and FE 200-600mm f/5.6-6.3 OSS G for BIF work. I am thinking of switching over to a R5 and RF 100-500mm f/4.5-7.1L IS. Originally I didn't consider it because of the slower available aperture of the 100-500 and also the shorter reach of only 500mm vs. 600mm.

Today I woke up and realized that with the A9's 24Mpixel (6000 x 4000) pixel sensor when compared to the R5's 45 Mpixel (8192 x 5464) sensor I can crop my images by ~1.36x and still get a 24 Mpixel image in post. This makes the 500mm give me the equivalent of 683mm equivalent if I only took out 6000 x 400 images.. So that removed one major barrier and now I know I can get a decent resolution out to 683mm.

The next barrier now though is the slower aperture at the log end of the lens. My calculations say that the Canon's f/7.1 is only 2/3 of a stop slower than the f/5.6 of the Sony. If that's the case can the R5 deal with the higher ISO needed to make up the difference?

The R5 + RF 100-500 together cost about the same as the the Sony A1 which I am also considering so its not a done deal other than neither the A1 or RF 100-500 are easy to find. There are other plus and minus between the two systems I am also taking in account and trading off. Currently shooting both but realize I am wasting a lot of money but I admit to being a gear head and enjoying the advantages of owning each system.

Please share your thought. Thank you for your time.

I used my friend's RF100-500 for one week,  as he wanted to try my 600MM F4.

RF 100-500 with R5, is really a good combination, no doubt about IQ or AF speed. because of its low weight, i can handheld for a very long time.

I go birding every day and i found for most handheld birders, earlier Sony A9+200-600 and Nikon D500+500pf are very common, now i can find Canon R5+100-500.