Seen as the A8 is a quad core, no matter how bad, you would probably see more improvement in getting the GTX 970 now and then eventually getting a new CPU, even a cheaper i5-4690/k would be a better cheaper option for you.
Getting the 970 will allow you to get better FPS in graphics demanding games, but you will experience a small bottleneck in terms of CPU power.
Seen as the A8 is a quad core, no matter how bad, you would probably see more improvement in getting the GTX 970 now and then eventually getting a new CPU, even a cheaper i5-4690/k would be a better cheaper option for you.
Getting the 970 will allow you to get better FPS in graphics demanding games, but you will experience a small bottleneck in terms of CPU power.
I agree with the Cheap Gamer, the 970 will probably give you the more noticeable performance boost, not to mention its also the cheaper and easier option. You won't have to get a new motherboard and reinstall most of your hard ware. Replacing a video card take less than a minute.