Well for £1,500 you could build something pretty beastly, probably 6700k+980Ti combo would be good - both of which are both easily overclocked and probably good for a number of years. The skylake chip might be a bit overpriced right now but its future proofing you in terms of the DDR4 options, there is also quite a range of good motherboards. The 980Ti is a solid card and a close match to a Titan performance in many cases with more future proof VRAM amounts over a 980 - for another £100-150 though.
You never really know what the future will bring but I can't see you regretting it in 3 years time... the only thing is the pending GPU Pascal launch, which is why i've got 1 980Ti in my recent build not 2 because i'm going to swap it out for a few of those if they do come out soon.
You'd probably be able to spec a number of options for the £500 more, question will always be how much you want to spend on the screen though... Potentially you may nudge the budget again because its always tempting to go for it if you are spending more on the hardware. I've just spent about £1600 on similar hardware, but with the addition of £450 in water cooling/£430 on a Dell G-Sync when it was boxing day sales. You could probably build the same hardware with closed loop cooling on the CPU (air on GPU) and compromise on a few areas to bring it in for about £1250 (i.e. PSU, RAM, MOBO, Case). Have a shop around, give it some thought, ultimately you probably use the PC daily so as long as you can afford the outlay you won't regret it...