Which GPU for £250?

[I cant post photos]

Asking for a friend really. He's got this:

Intel Core i5-6600K 3.5GHz Quad-Core Processor

Cooler Master Seidon 120V Liquid CPU Cooler (TBC)

Asus Z170I PRO GAMING Mini ITX LGA1151 Motherboard

8GB (2 x 4GB) DDR4 Memory (TBC)

Samsung 250GB 2.5" Solid State Drive (x2)

Cooler Master Elite 120 or 130 Mini ITX Tower Case

EVGA SuperNOVA G2 550W 80+ Gold Fully-Modular ATX Power Supply



Wants to know the best bang for £250. Any ideas?

 

[I cant post photos]

Cheers all, I'll give him your ideas and let him decide what he wants