i would like to add to you discussion despite the fact that there is a chip shortage.
Performance wise the RTX 3080 will outperform the A4000 by far.
If you want to compare the cards, the Keyshot Viewer comes with a Benchmarking tool specifically for KeyShot, that way you can be sure the render settings are the same.
We managed to find this article https://aecmag.com/workstations/nvidia-rtx-a4000-review-nvidia-rtx-a5000-review-arch-viz-ray-tracing/
where the A4000 scored a 62.34.
Compared to the RTX's 3080 results of 70.83 found here https://forum.keyshot.com/index.php?topic=27020.msg114277#msg114277
, it gets clear that the 3080 will give you better performance.
If you run a benchmark yourself feel free to upload the results in the Benchmark section: https://forum.keyshot.com/index.php?board=36.0
Note that the used driver version can make a difference, so your results might diverge a bit.
Keep in mind that the mount of memory will limit the size of scenes you can render. If you often work with models of Large industrial machines, high resolution texture-maps or frequently use the geometry shaders(e.g. displacement and Fuzz), having more memory will give you more headroom.