Do you mean with a 4k screen, or suitable for editing 4k media?
www.xoticpc.com is a good site to check out several higher end systems at once, for what you want I'd maybe go with a workstation over a gaming system, but a good gaming system will be good as well since they will have quad core i7 CPUs and fast video cards.
Best thing would be a desktop though, I'd go for that unless you really need a portable system. With a desktop you can get another 20-30% speed increase for the same price.