Even now in 2015 the i5 2500k is a fantastic quad core chip (all the intel quad cores since sandybridge are fantastic gaming cpu's) and unless you want something for intensive video editing i would stick with the i5 2500k. To answer your question directly, NO, it shouldn't bottleneck the gtx970, the only bottleneck will be if you don't have sufficient memory.
My advise would be to stick with your current cpu for at least a couple more years as upgrading now for gaming purposes would be pointless. You could always upgrade the memory you use and motherboard but broadly speaking the graphics card and memory the the key components for gaming and the i5 2500k even at stock speeds is more than sufficient for gaming.