Playing at 3440x1440p means you'll be more GPU bound than CPU bound. Games that are CPU-bound aren't really CPU-bound so much as single/dual-core bound. What this means is that unless you're looking to do a Quad SLI going the Haswell-E route is a waste of money. Challenge anyone that's advising you to do that to back up that advice with real world benchmarks at that resolution.
If you click here for 4K benchmarks you can see that CPU is pretty irrelevant at this resolution so long as it's at least i5. This means that buying anything other than an i5 4690K is a waste of money. Except if you want to run 4 GPUs (which I wouldn't recommend anyway) or do some other serious CPU-heavy tasks, but that's not gaming.
As for the GPU, it's a toss-up between the R9 295x2 or the Titan X. If the games you play have crossfire profiles then the 295x2 is a much better choice than the Titan X since it has both better performance and is cheaper.
Lastly, rules of thumb are: Any RAM is fine, speed makes no difference for gaming performance and DDR4 is overpriced and pointless for gaming.
Motherboard-wise, most 100 pounds boards can achieve good OCs and do crossfire/sli and also have M.2 slots.
For coolers, most good air coolers are around 50 quid (I like phantek ph-tc14pe most) and the closed loop coolers are simply more expensive for the same performance but look cooler (I guess).
For SSDs I'd avoid Samsung for now as they've had a few controversies with their EVO series and it's not worth the hassle when equivalent alternatives are available (Crucial ones are pretty good).
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