You're still recommending they spend
more money, when it'll only benefit game performance. By all means make a case for the A8-7600 as a cheaper option; that makes sense (although I suspect the OP will still opt for the 7870k as the most powerful desktop APU available), but I don't see why you're so set on persuading the OP to spend more money on a set up that will only do one thing better, when that thing is something they're not that bothered about...?
EDIT:
Depends what you mean by best contender
The 7870k is the most powerful APU, and has an unlocked multiplier so is easier to overclock if you decide further down the line that you want to get a discrete card and push the performance up.
You could save yourself ~ £7 by going for the 7850k or 7800 - they're both clocked lower than the 7870k: the 7850k is also unlocked for overclocking, while the 7800 has a lower TDP and therefore should use less power and produce less heat: but the Hexus review found it was almost identical to the 7850k in power draw!
Ignore the A10-7700k; it's been superceded by the A8-7670k; this has less GPU shaders than the A10s (384 vs 512) so the graphics isn't as potent, but the CPU is pretty much the same and again is unlocked for ease of overclocking. That's currently £82, so you'd see a > £20 saving if you went for that.
Finally, the A8-7600 is the darling for many people. Again it's got the second-grade GPU with only 384 shaders, and it's lower clocked on the CPU than the others, but it's still a decent quad-core APU and it's currently only £66, making it exceptional value.
For my money, there's no real point going for anything between the A10-7870k and the A8-7600: the 7850k and 7800 are too close in price to the 7870k, and if you're not getting an A10, the unlocked multiplier on the A8-7670k probably isn't worth the £18 premium over the A8-7600.
The 7870k is flat out faster than the 7600; more GPU shaders and higher clock speeds on the GPU and CPU. Theoretically that means it will use more power and generate more heat, but a lot of reviews show there's not that much difference in real world usage. OTOH, the 7600 should be more than adequate for light gaming at low settings, and the £40 price difference is pretty significant at this end of the market.
So really, it's down to whether you think that a little extra performance (because as Endless say, no APU can rival a discrete card in gaming) is worth the extra £40 to you....