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 have a9, a1 and 200-600 and recently used the R5 100-500.  Some observations when compared to A1.

R5 combo seems to have more saturated colours and slightly better contrast and maybe a bit sharper.  Colours seem quite a bit easier to work with in post.  Contrasts/sharpness is pretty marginal at best.

R5 animal/bird af is excellent but the a1 tracking seems to be better with slightly fewer misses when shooting bif.  Both over 90% so pretty marginal and obviously 30% more frames to choose from for A1.

200-600 is not really 600 so actual reach difference is not so much.  However Both a9 and a1 work extremely well with the TC1.4 at 840mm.  R5/100-500 at 700 maybe not so much.

200-600 does not extend, quite a bit heavier and has nice short zoom throw.  100-500 on the other hand is super light and more flexible with 100-200 range for landscape, self video etc.

So when considering R5 I would think about it vs A1. But no contest when compared to A9 or A9ii.  They can't compete with the AF system or lack of megapixels.  In video mode none of the Sony's can compare with the Canon for animal/bird af tracking - they don't have it at all.