Thinking it all over, if, as I predict, I can only budget for £1k, I'll go i5 and keep it under. There's a chance that I may be able to squeeze a few more quids out of the stone between now and when I want to purchase. If so, I'll be happy to spend the extra £300 or so to get a decent i7 build.
But one has to be careful! This all started 6 months ago when my PC started to die: I originally planned to buy a "no more than £400" laptop to replace it. But then I got thinking... I fear there may be no limit! I have to buy as soon as I can just to stop myself from going any further!