I don't have a desktop, and I've been thinking recently about not getting a laptop and getting a desktop pc instead (easy to upgrade as time goes on n stuffs)
Build it yourself! Trust me it is easy, I built mine and I currently duel wield 2 GTX 1080's with an overclocked intel I7 6800k cpu and 16gb corsair DDR5 ram. I have a 2tb ssd (I believe it is SATA without looking.) The mother board was an Asus ITX H87 capable of 4k performance. The total cost was somewhere above £1,500 (Not including duel 27" acer monitors or keyboard and mouse.) If I was to purchase something of that tier I would assume the total cost would be around £200 - £600 more expensive.
I agree with Ice, most already assembled PCs that have newest technology in them are fuckin' expensive, so you better build one yourself, it will be somewhat cheaper. Assembled Hi-Tech PCs cost around 1500+ €. 850£ are around 995€. Also, Overwatch and Just Cause 3 do not need a GeForce Gtx 10 series video card. You can take a 980.