Want to apologise for this lazy post, first of all, not going to provide links
As others have said, really not worth the extra cash for an i7 just for gaming purposes. The i5 6600K got really good reviews with many likening it to the 2500k in that it should last a long time, overclocks well, is a decent jump up from the previous generation and sits at a good price/performance. For many still on the 2500k, THIS is the one that's got them to finally leave it behind. If you're going to OC, you'll need a cooler better than the stock one that is bundled with the chip.
As the 6th Gen uses the 1151 socket, you'll have access to DDR4 RAM - Previously RAM speed has been a bit of an afterthought, but benchmarks have shown that this latest iteration has a really positive impact on frame rates. I'm seriously considering going right the way up to 3000MHz this time, 16GB of it.
For a motherboard you'd need a 1151 socket again, so a Z170 would be the best choice. You will need the Z model to OC the CPU and run the faster RAM.
GPUs aside from the CPU, is the biggest choice (and most expensive). The new Nvidia cards look great, as do the AMD cards. Given the cost of everything else I've mentioned, plus a case and PSU, we're probably halfway through your grand. It makes little sense to spend it all on a GPU if you've got one small 900p monitor. For Nvidia, there's a big gap in price and performance between the 970 and the £400 1070. The new AMDs might fill the performance gap with a price comparable to the 970 (approx. £230). It could be worth seeing how they perform before pulling the trigger.
Personally I would never leave a 2(+) monitor setup. So if I didn't have anything suitable I'd pick up 2x 24~ inch monitors (approx. £100 each) and then either a 970 or one of the new Polaris (AMD) cards, depending on benchmarks. I feel a 970 (or Polaris) and a one fancy (4k or gsync, you'll struggle to afford both) monitor is probably also doable, but possibly tight. The monitors are still quite pricey and I've never had one to see if they are really worth the cost. If you have a decent monitor already, consider the 1070. It's around £400 though, which is a good deal higher than I would personally pay (maybe... ) as the price to performance ratio ordinarily drops off at around £250 for GPUs. The benchmarks are impressive and it outperforms the similarly priced 980Ti.
EDIT: So I forgot Hard Drives. Even SSDs have dropped significantly in price recently, but my personal favourite (if we reserve £200 for the GPU) is the ridiculously fast range of PCIE SSDs. Not cheap, at £300~ for 400GB, but ridiculously fast. At over 2GB/s read speed... it's ridiculously fast.
More seriously though, half a TB of SSD should be around £100, look for decent read/write speeds, and a further £100 will get you around 3TB of traditional spinning HDD, 7200RPM is optimal. I personally have a hybrid, but given how much lower the prices are at the moment, I wouldn't recommend it.
Edited by Salamol, 26 June 2016 - 12:52 am.