GTX 970 vs R9 380

Solution
The GTX 970 is much better than the R9 380, which is just a slightly better rebrand of the R9 285. 4GB of VRAM is a good amount, as it has just enough headroom to support maximum textures.

Woody

Woody1999

Admirable
The GTX 970 is much better than the R9 380, which is just a slightly better rebrand of the R9 285. 4GB of VRAM is a good amount, as it has just enough headroom to support maximum textures.

Woody
 
Solution

Woody1999

Admirable
The AMD card will perform slightly better than the GTX 970 at 1440p and up, and will perform equally or slightly worse at 1080p. It also uses a lot more power, needing a good quality 600W power supply to support it.

Woody
 

anti-duck

Honorable
That is a really nice build :) The 4590 is perfect, it's one of the best CPU's in terms of price:performance. You might be able to save a bit of cash on the motherboard by going for a lower end chipset and enquiring with the retailer if they would update the BIOS for you prior to purchase, otherwise, you're limited to H97 or Z97.
 

Woody1999

Admirable
Don't tell anyone I told you this, but you can get genuine retail Windows keys on r/microsoftsoftwareswap. They go for $10, which is about £6 in real money ;)

Here's what I would change, taking into consideration the money saved on OS:

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-4590 3.3GHz Quad-Core Processor (£154.92 @ Aria PC)
CPU Cooler: Arctic Cooling Alpine 11 Pro Rev. 2 36.7 CFM Fluid Dynamic Bearing CPU Cooler (£6.62 @ Amazon UK)
Motherboard: Asus Z97-P ATX LGA1150 Motherboard (£59.51 @ CCL Computers)
Memory: Kingston HyperX Fury Black 8GB (2 x 4GB) DDR3-1600 Memory (£41.73 @ Ebuyer)
Storage: Samsung 850 EVO-Series 120GB 2.5" Solid State Drive (£47.99 @ Amazon UK)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£32.40 @ Aria PC)
Video Card: Gigabyte GeForce GTX 970 4GB WINDFORCE 3X Video Card (£259.00 @ Aria PC)
Case: NZXT S340 (Black) ATX Mid Tower Case (£49.98 @ Scan.co.uk)
Power Supply: XFX 550W 80+ Bronze Certified ATX Power Supply (£46.18 @ CCL Computers)
Wireless Network Adapter: TP-Link TL-WN881ND 802.11b/g/n PCI-Express x1 Wi-Fi Adapter (£12.95 @ CCL Computers)
Monitor: Asus VE247H 23.6" Monitor (£109.90 @ Amazon UK)
Other: Microsoft Windows 7 Home Premium N (£6.00)
Total: £827.18
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-07-04 00:13 BST+0100

Added a dead silent cooler to go with your CPU, I have one myself. It keeps my Q8300 cool overclocked to 2.9GHz, and doesn't make a sound even at full speed. I've also changed the graphics card to a better model (Windforce cooler) and changed the case. Unfortunately, the Phantom 240 is a pretty bad case. NZXT tried to stuff all of the Phantom goodness into a cheap case and it just turned out to be poor quality. I also got you a bigger monitor, which is probably the best size for 1080p monitors.

The biggest change is including an SSD in your budget. A 120GB SSD and 1TB hard drive is much faster than an expensive 1TB high-performance drive. The Samsung 850 Evo is probably the best budget SSD on the market, excluding the little-known OCZ ARC100.

Woody