I think it’s mainly a budget thing and weather or not you’ll do renders yourself or for example upload the files to a dedicated render farm.
Personally I think the ‘gaming’ PC is a better pick currently than most offered ‘workstation’ solutions but that’s also about budget. If you are going to do renders over GPU it need a lot of money to have a Nvidia pro GPU solution being as fast as the speed a 4090 offers.
The advantage of the pro series though is that most you can link using NVLink which will also expands the VRAM. The 4090 has no NVLink support so you can drop 3 of them in a PC which will render 3x as fast as a single 4090 but the VRAM is still limited to 24GB.
24GB is quite a lot but it really depends on how much textures you use or what resolution you render on how fast you run out of VRAM.
If you have budget than it’s great to have some workstation with multiple GPUs which have custom liquid cooling (keeps it quiet). HP doesn’t offer such solutions I think since they are way to specialized and have a limit target audience but for example systems like this would be amazing: Studio Series Liquid-Cooled Workstations for Content Creators – EK Fluid Works
The price will consist a lot of the GPUs you use. The 4090 is best in price performance, you get a lot of CUDA cores at one card for a ‘relative’ cheap price. While the 3090(Ti) still could connect multiple cards using NVLink NVidia ‘discarded’ that option on the 4090 because they like to push people into the pro series.
I think that only makes sense if your scenes are really that big. Especially because a lot of pro cards have actually less CUDA cores than a 4090 so it gets pretty expensive if you want to get the same render speed.
If the 24GB is not really an issue with the kind of renders you make you could go as crazy as a system like this, 4 (or up to 6) liquid cooled 4090s and a lot of jealous colleagues. BIZON Z5000 – Liquid cooled NVIDIA RTX 4090, 4080, 3090, A6000, A100 Deep Learning and GPU Rendering Workstation PC – 4 GPU, 6 GPU, up to 56 cores Intel Xeon W (bizon-tech.com)
If your renders contain a lot of metals without textures the VRAM usage is not as high as if you would apply a very high res rough/base color/normal map texture on every part of your assembly. So before spending the money it’s good to examine some scenes and check how much VRAM they actually use.
If you need to get HP I would go for the Omen series if that’s still a thing. I wouldn’t be happy with the Nvidia A2000 6GB card. That might be called pro but if it’s about renders, better continue in gaming mode 
The solution of EK Fluid Works is a nicer one in an office environment, the 4090 can make quite some noise if it’s not liquid cooled.
About the CPU, I’ve a 4 y.o. i9-9900K but that doesn’t matter much while rendering using my 3090+4090. It does while playing MSFS, than a better CPU would be nice 