I think this would be very near optimum..
The SLI-capable Asrock Extreme3 ranked 58 would be nearly impossible to beat vis-a-vis price/performance..
http://motherboardbenchmark.net/best-chipset-intel-z170-motherboard-october-2015/
PCPartPicker part list: http://uk.pcpartpicker.com/p/j9YzKZ
Price breakdown by merchant: http://uk.pcpartpicker.com/p/j9YzKZ/by_merchant/
CPU: Intel Core i5-6500 3.2GHz Quad-Core Processor (£164.28 @ Aria PC)
Motherboard: ASRock Z170 Extreme3 ATX LGA1151 Motherboard (£106.08 @ More Computers)
Memory: G.Skill Ripjaws V Series 8GB (2 x 4GB) DDR4-2400 Memory (£32.21 @ CCL Computers)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£37.98 @ Novatech)
Video Card: Sapphire Radeon R9 390 8GB Nitro Video Card (£275.99 @ Overclockers.co.uk)
Case: Deepcool TESSERACT SW RED ATX Mid Tower Case (£29.99 @ Ebuyer)
Power Supply: XFX TS 650W 80+ Gold Certified ATX Power Supply (£66.09 @ Amazon UK)
Total: £712.62
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-05-31 22:04 BST+0100