a custom built desk top can deliver huge performance advantages at affordable prices, particularly if you are into heavy image stitching or stacking.
I stack and I stack 36MP layers, sometimes 150 at a shot. I use Zerene Stacker, but there are others that work too.
As for computers, I stopped buying premade computers systems years ago and began having them built for the specs we need to process stacks, panos, video, etc. I am on my third custom-built computer and each has been increasingly expensive, because time is worth life, and I am getting older.
It is one thing to have a fast computer, but you need software that can access that speed as well, especially with graphics. IMO, forget about building your own. Even forget about having the local computer guru build one for you. Spend some money and have it tuned to what you actually need. I had one built by Boxx. It worked, but the staff there tried too much to upsell me with B.S.. Even tried to tell them to desist, but they were just rude.
The best company I know of is Puget Systems, out of Auburn Washington.
https://www.pugetsystems.com/This company and the folks who work there are beyond what we can expect. They even call and re-tune your system, as well as provide a complete notebook with backup disks, photos of your particular system, and every last part on it. I cannot recommend them enough. That’s the good news.
The bad news is no different than any of these companies. These fast computers cost money and a lot of it. They have to be budgeted just as we budget money for cameras and lenses. At this point I have a very fast system, but it is still too slow sometimes. I have several Macs, but I only use PCs for photography because I find they are faster, less expensive, and more easily interfaced to peripherals.
Right now I am using a water-cooled system based on:
Asus X99 Deluxe Motherboard
Intel Core i7 5960X 3.0 GHs eight-core 20MN 140W (overclocked) CPU
128 GB DDR-4 2133 REG ECC RAM
Dual PNY Quandro K5200 PCI-E 8GB GPU video cards
And a variety of internal SSD and SATA drives, connections, etc.
The bad news is that it cost more than $10K....
This machine does well with still and video photography, but is IMO still held up by Adobe’s software, as far as I can tell. Here are some photos.