This thread has been running in The Lounge forum for a couple of days, and it makes some interesting points. Worth a look see if are considering a computer upgrade any time soon. Or later come to that. Some of the links are centred around Video Editing systems, but a system designed to work well with NLE is going to totally fly with Photoshop. There is also a link to a Mac Pro vs PC workstation article, that underlines the advantage of a custom PC if you need to go really high end at a sensible price.
There is a very big difference between Video editing and image editing. Video editing requires more machine than image editing.
Self build every time for me. Built my current PC in 2013 - but I'm still pleasantly surprised at how well it handles video (Premiere Pro/After Effects) and 3D (Photoshop and Blender).