The 260X is going to limit game performance in newer or more demanding games no matter what CPU you have.
Right now, if I was you, I'd use something like MSI Afterburner to monitor CPU and GPU usage in the games you play. Depending on the games you play, you might see CPU usage well below 100%, with GPU usage at or near 100%. This would confirm that your 260X is what needs to be upgraded.
You don't say why you want to upgrade, so I'm guessing it's game performance at 1080p. Also, depending on what videocard you choose, you may need a better power supply.