Best cost performance GPU for Network rendering?

[Higuchi]

Hey guys,

I always appreciate the performance of Keyshot Network rendering. I'm thinking that I want to improve its performance much more with high spec GPUs.
Which Graphic Board is the best not only for performance but also cost? Since I'm using RTX-4000 in local environment now, I think it's better also for network rendering. So, I'm going to buy extra three RTX-4000 or RTX-6000. Could you advise me, if you would have another tips for GPU? Below is one of my references.

https://www.nvidia.com/content/dam/en-zz/Solutions/design-visualization/solutions/rendering/proviz-print-keyshot-solution-brief-us-1232870-r5-web.pdf

Thank you,