Spirit is being a noob. A i5 and 780 will be much better in the long run then a i7. For example, look at a i7 2600K and 580, or a 2500K and 570. Look at the benches, that will be what it's like for a 4770 and 770 and 780 and 4670K. A easy example is: 570 and i7 are worse in Crysis 3 by at least 30 percent then 580 and i5. That is what it will be like with a 770 and i7 over i5 and 780.
@wrxengland - just get the i7 and the 770. Seriously mate, look at the benches I posted earlier which compare the 770 and the 780 - you have to ask yourself is the 780 is really worth the extra £200, and the answer is no, it's not. This is usually the case for the higher end cards, the 'second best' cards are nearly always better value than the highest end cards on the market.
I'm not saying the i5 won't do the job, it will, but you've got £1,500 to spend, and yeah you could argue that you could get the 780 and only be £80 or so over budget, but you want to spend it wisely, and not waste £200 on things which won't make much of a difference.
If it was me personally, if I was doing gaming or something else quite intensive, and I had £1,500 to spend, I'd get an i7. I know the i7 doesn't make much of a difference in most games, but some games are more CPU intensive, which Okedokey pointed out.
At the end of the day, you can get an i7 4770K and 770 for £1,300 and have a cracking system. Why not go that route and end up with an awesome system but still be £200 under budget? By getting an i5 you'd only be cutting about £100 off your system. Who knows what you might want to do in the future though?
Usually it is best practice to recommend spending more on the GPU than CPU for games, and that is usually what I do, but a 4770K and a 770 is by no means going to be 'under-powered' at all. A 770 is about as powerful as the 680 and that is a powerful card and both will continue to be more than enough for a while. By buying the 780, you're not getting much more at all for your money and by the time you need to replace the 770, you would also need to think about replacing the 780 too because the performance difference between the 770 and 780 isn't huge - but the price difference is.
@PCunicorn - 'an i7', not 'a i7', ok?
just over the budget but what the hell lol shame spirit your not closer to me u could build it for me .any chance u can move to rotherham ,