PixInsight eats up CPU cores, RAM and I/O. The more you can throw at it, the better off you will be. Linux helps. The difference between a Windows and Linux machine is around 5-10%. The offset can be lowered (on Windows side) by adding more RAMDisk, but there is a cost associated with that as John points out.
I am building a system right now with the following specs -
CPU - AMD Threadripper 3960x (24-cores with 48 threads). I won't be over-clocking the CPU. I haven't found a real need for that.
RAM - 128GB @ 2933MHz, once again, not going to overclock it.
GPU - I am going to be using my old GPU (GeForce 1030). I don't use Starnet, and PI does not use CUDA cores for anything else. So, there will be no real loss in compute power for me.
Hard Drive - 2TB M2.2880 SSD.
OS - Kubuntu 20.10 (I might fall back on Ubuntu, but I want to give KDE Plasma desktop a shot).
Now, to peel the onion a bit more -
As you can imagine - I/O speed helps when you read/write files. Especially if you have a camera that creates 120MB files - this is really important. For cores/threads to be useful, the underlying process needs to use multi-threading. ImageIntegration uses multi-thread processing. If you have multiple files, each file will be given its own thread for processing. ImageIntegration also uses a lot of RAM just because each thread, after processing each file, has to pass back that information back to the "mother-thread" - if the mother-thread is busy, that information then has to be cached in the RAM. If you have a camera with a large number of small pixels, the RAM gets used pretty fast - the more you have, the better off you will be.