Your motherboard is socket FM2+, and will take any socket FM2+ CPU - for instance, Athlon 860K or A10-7800. FM2+ has only very low-end CPUs, and any of them will bottleneck a GTX 970. Is it possible for you to sell/return the motherboard and get an Intel socket 1150 or 1151 motherboard instead? If not, I would recommend an Athlon 860K if you're overclocking, or an Athlon 845 if not, but bear in mind that there is no upgrade path for your board and you'll be CPU-limited from day one.