Totally, you are welcome! It'd be nice to hear what other people have to say as well :)
So the 8700k used to be the top of the line for single threaded performance but not a strong performer for rendering at all - We are talking way slower than even a 2920x from last gen AMD. The 8700k is essentially a consumer chip so anything from the HEDT line (Threadrippers + i9s) will trounce all over it in rendering speed. If I recall correctly the more fair comparison between the chips would be the 2700x / 2600x Ryzen against the 8700k.
The 3950x is an amazing chip in my opinion for the perf / $ minded folks. It offers fairly close to 2990wx performance (roughly speaking - 54s to 45s) but it costs way less plus the platform as a whole is cheaper.
For comparison, the 3950x should be a bit more than twice as fast as the 8700k. In terms of render times (both final frame and IR) you are looking at the rendering times going from 1 minute to about 30ish seconds if you upgrade from the 8700k to the 3950x.
Considering that your 8700k is in a laptop it is also probably thermally constrained (its a desktop chip in a laptop) so the difference is probably even more than that.
I think going with the 3950x or the 3960x is a good choice and depending on how much you can spend as both are imho great options for what you pay in that particular price bracket. They both offer top notch single threaded performance too, not just the all core extravaganza.
2990wx, great for rendering, less great for some other stuff due to its architecture and memory related drawbacks. Still, I know a lot of people who use it and are super happy with it. Still, I'd personally only go with the 2990wx if I can get it cheaper than the 3960x which I don't think you can at the moment - at least not from any sellers that I know (including Ebay).