im not a big fan of the 3 core, or 6 core. i like my stuff in multiples of two. The pricing on those are very similar, as well as performance. http://www.tomshardware.com/reviews/cpu-gaming-performance,3007-5.html
the chart her has them basically as the same thing.
if it were me, i guess i would go with the 970, and OC some. if i felt i needed it. i currently have a 965, running stock at 3.4, i think the 970 runs 3.5 stock.