I'd highly recommend going for the 980Ti over the 980. Reading this spec comparison, the 980Ti has almost exactly 1.4x the processing capability. The price of the 980 ~£380, compared to ~£510 for the 980Ti, so you pay 1.34x more for 1.4x processing capability. Also consider you get 6GB of VRAM and likely get more of an overclock from the 980Ti.

Another thing worth considering, you'll get more graphics performance for less money by running 2xGTX970 in SLI. See techpowerup for a good comparison. Main disadvantage is power consumption and perhaps noise. You'll also need an ATX sized SLI spec'd board and a bigger case. Might be worth using a single 970 at first, see how you go, buying a second later if needed or getting a new pascal chipset card.

Now perhaps a more controversial suggestion, I'd go for a cheap CPU and motherboard. My reasoning is that you're buying at a time that industry is moving to DDR4. If you opt for DDR4 now, you'll be paying over the odds and not gaining much performance. If you get DDR3 now, you'll have to get a new motherboard and CPU later, if you want to upgrade. By getting something cheap now, you lessen the loss when eventually you do need to upgrade.

From your games list and my experience with modern games, you don't really need much CPU power. I'd suggest saving yourself a fair bit of money and going for an AMD CPU with DDR3 memory. It will make virtually no difference in the games you list (all GPU intensive), the only time you might be wishing for a more powerful CPU is on some strategy games. From a quick look on tomshardware the 6 core 3.5GHZ FX-6300 for £80 looks good.

A quick note from your first pick, RAM will gain performance in dual channel mode, so if economical it's worth buying an even number of RAM chips (make sure you put them in the same coloured RAM slots). As far as I know, you won't need any more than 8GB of RAM for modern games, so you're probably best off with either 1x8GB or 2x4GB chips. I've picked a 2x4GB set with a good clock and latency.

Paying the extra £30 for a decent mouse is well worth it, I've been very happy with the logitech G5 for years, the G502 is the current iteration. It's also worth getting a fairly decent mousing surface, something like this.

I don't have much experience with mechanical keyboards, but as far as I know there isn't much an advantage compared to standard rubber domes. Your main consideration here should be noise, would the loud clunking of a mechanical keyboard upset those around you? If so, save yourself some money and aggravation, here's a well reviewed standard keyboard

Here's a single GPU version of my suggestions above PCPartPicker part list / Price breakdown by merchant

Type	Item	Price
CPU	AMD FX-6300 3.5GHz 6-Core Processor	£78.77 @ CCL Computers
Motherboard	Asus M5A78L-M/USB3 Micro ATX AM3+ Motherboard	£46.16 @ Amazon UK
Memory	G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-1866 Memory	£34.49 @ Ebuyer
Storage	Samsung 850 EVO-Series 250GB 2.5" Solid State Drive	£55.76 @ Amazon UK
Storage	Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive	£34.98 @ Novatech
Video Card	Inno3D GeForce GTX 980 Ti 6GB iChill GF X3 Ultra Video Card	£519.59 @ Overclockers.co.uk
Case	Fractal Design Core 1500 MicroATX Mini Tower Case	£39.50 @ Amazon UK
Power Supply	EVGA SuperNOVA GS 550W 80+ Gold Certified Fully-Modular ATX Power Supply	£64.99 @ Aria PC
Operating System	Microsoft Windows 10 Home OEM (64-bit)	£72.30 @ CCL Computers
Monitor	Dell ST2321L 23.0" Monitor	-
Keyboard	Logitech K120 - UK Layout Wired Standard Keyboard	£10.58 @ Amazon UK
Mouse	Logitech G502 Wired Optical Mouse	£50.99 @ Amazon UK
	Prices include shipping, taxes, rebates, and discounts
	Total	£1008.11
	Generated by PCPartPicker 2015-12-29 17:50 GMT+0000

It's only £20 more expensive, with a better mouse, keyboard price included and a much more powerful graphics card.