Not to disagree, but i think you might be overthinking the 'IQ gap' between the big primes and the zooms. honestly, for about $1,900, the Sony FE 200-600mm f/5.6-6.3 G OSS is basically the king of value. i mean, yeah, the Sony FE 600mm f/4 GM OSS is incredible but it costs like $13,000... thats a massive price jump for detail most wont notice. the 200-600mm handles the Sony Alpha 1 Mirrorless Digital Camera resolution just fine and still hits those high burst rates on the Sony Alpha 9 III Mirrorless Digital Camera. plus, that internal zoom is sooo much more practical in the field compared to a fixed prime. id say save the $11k and maybe just grab a Sony FE 1.4x Teleconverter SEL14TC if you really need the extra reach. gl!

Oh man, congrats on that dual-body setup!! Honestly, that's basically the dream team for wildlife right now. I've spent way too many hours in the mud with various setups over the years, and I totally get the dilemma... it's a struggle to find that 'perfect' balance between reach and speed. In my experience, here's how the different paths have worked out for me: * **The internal zoom:** I used the popular internal zoom for a couple of years because it's just so convenient. Not having the lens barrel move when you're zooming in a tight spot is huge. But, tbh, once I got a high-res body, I started noticing it didn't quite have that 'magic' sharpness I wanted for heavy crops. It's a fantastic lens, but maybe not the one that lets a 50MP sensor truly scream.
* **The fast f/2.8 prime:** This was a total game changer for me. I lowkey prefer the versatility of the f/2.8 glass because you can throw on a 1.4x converter and basically have two lenses in one. It's lighter than you'd think, and for fast mammals at dawn, that extra light is everything. I found it tracked way better during high-speed bursts too.
* **The long f/4 prime:** I've borrowed the big 600mm-style f/4 a few times and yeah, it's the gold standard for a reason. The background blur is literally butter. But for me, it was just too much to haul around for long days. I felt like I was tied to a tripod, which kinda kills the fun of a fast setup. So yeah, based on what I've learned, I think the fast f/2.8 prime approach with converters is the absolute winner for your situation. It's what I ended up keeping because it handles those insane autofocus speeds so well and gives you that extra reach when you need it. It really lets those high-end sensors do their thing without weighing you down too much!! Good luck with the decision, it's a fun problem to have lol. Cheers!

ngl i totally agree with what's been said about the value of the 200-600, but coming from someone who has spent years out in the bush - u really need to think about the reliability of the whole rig, not just the sharpness. When ur pushing these high-end bodies like the a1 to their limits, there are some 'hidden' traps that can ruin a trip. - Mount stress: honestly, the weight of the heavier glass can really strain the body mount if u aren't using a high-quality replacement foot. Don't trust the stock ones if ur hiking miles with it!!!
- TC swapping: iirc, constantly adding or removing teleconverters in the field is basically an invitation for dust to hit that sensor. With 50MP, every single speck shows up and it's a total pain to clean later.
- Weather sealing limits: even with 'pro' gear, none of it is truly waterproof. I've seen seals fail during heavy humidity shifts, especially around the zoom rings or the mount gasket. Basically... just be careful about the mechanical side of things so ur gear doesn't fail when that rare bird finally shows up???