Which build would run games at 4k the best?

Solution
The second build. The better GPU will give higher FPS at 4K and both CPUs will be bottlenecked by the GPU. So better to get the 1080TI and the 1600 than the 1080 and the 1700.

However i did a small change to give you a much better PSU for just around £5-6 more. Whit a high end system like this, you don't wanna go cheap on the PSU, specially if you are going to overclock the CPU. Also you don't need 750w.

PCPartPicker part list / Price breakdown by merchant

CPU: AMD - Ryzen 5 1600 3.2GHz 6-Core Processor (£178.50 @ Amazon UK)
Motherboard: MSI - B350 PC MATE ATX AM4 Motherboard (£79.98 @ CCL Computers)
Memory: Kingston - FURY 16GB (2 x 8GB) DDR4-2400 Memory (£121.98 @ Ebuyer)...
The second build. The better GPU will give higher FPS at 4K and both CPUs will be bottlenecked by the GPU. So better to get the 1080TI and the 1600 than the 1080 and the 1700.

However i did a small change to give you a much better PSU for just around £5-6 more. Whit a high end system like this, you don't wanna go cheap on the PSU, specially if you are going to overclock the CPU. Also you don't need 750w.

PCPartPicker part list / Price breakdown by merchant

CPU: AMD - Ryzen 5 1600 3.2GHz 6-Core Processor (£178.50 @ Amazon UK)
Motherboard: MSI - B350 PC MATE ATX AM4 Motherboard (£79.98 @ CCL Computers)
Memory: Kingston - FURY 16GB (2 x 8GB) DDR4-2400 Memory (£121.98 @ Ebuyer)
Storage: Seagate - Barracuda 2TB 3.5" 7200RPM Internal Hard Drive (£53.50 @ Aria PC)
Video Card: Asus - GeForce GTX 1080 Ti 11GB Turbo Video Card (£660.00 @ Aria PC)
Case: NZXT - S340 (Black/Red) ATX Mid Tower Case (£64.99 @ Novatech)
Power Supply: Corsair - RMx 650W 80+ Gold Certified Fully-Modular ATX Power Supply (£84.11 @ Ebuyer)
Monitor: Samsung - U28E590D 28.0" 3840x2160 60Hz Monitor (£299.00 @ Amazon UK)
Total: £1542.06
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-10-23 18:36 BST+0100
 
Solution