The Athlon x4 760k for $90 is your best bet. It would only be a minor upgrade from your A10, but it will overclock a good bit higher assuming you have am A75 or A85 chipset, and a good aftermarket cooler. I know the 6800k usually overclocks a lot better than the 5800k so the 760k should overclock pretty well too.
But honestly, you have picked a bad platform for a 7970