If you can wait till the mid of September then I'd say get the 860k. Or if you just want to get something now, then get the 760k.
EDIT: Btw, don't buy Windows 8.1 from there, get it from G2a for really cheap. Or from Reddit for even cheaper! And throw the left-over money on a better GPU. Preferably the 270 in this case.
Links: https://www.g2a.com/windows-8-professional-32-64-bit-cd-key-global.html
http://www.reddit.com/r/softwareswap/