The A10 does not win, and it runs hotter at any frequency, because it also has an integrated graphics processor. The 860k does not.
The STOCK clock speed on the 7890k is definitely faster, but it's also more than twice the price. Unless you plan to NOT use your GTX 970 and TO use the integrated graphics, you're mostly paying double, at least, for something you won't even use.
And by the way, the faster clock speed on the 7890k, which allows it to barely nudge out the 860k and 880k, is a factory overclock anyhow, so you're aren't avoiding anything and you're paying double for something you could do yourself for free. I'm not sure what idiot's remarks you were reading on wherever you read that about overclocking, but the only way you would shorten the life of your CPU or damage it in any way from overclocking is if you weren't paying attention to what you were doing, or were just clueless, like that guy might have been, and either used too much voltage (Beyond what the cooling being used could accomodate) or had a less than satisfactory cooler installed.
Myself, and just about every other long time member of this forum that I know, have been running HIGHLY overclocked systems for 5-10 years on the same CPU with no adverse effects. I have clients I built systems for and configured overclocked settings on 5+ years ago, several of them, and all those systems are still running fine, probably beyond their useful life for that matter. But whatever you think is best for you. Personally, I'd rather pay 70 bucks for a 3.7Ghz CPU for that platform than 159.00 for that A10 that offers about 4% better performance than the stock 860k. If an extra almost 100 bucks is worth it for a 4% gain, to you, then by all means, go with it.
It offers NO better performance if you overclock the 860k to 4.1Ghz, which is WELL within it's capability. You could probably go as far as 4.5-4.8Ghz with a good cooler.