my personal experience with FPS drops was that the actual game was conflicting with some software on my pc.
Make sure the GPU has the latest drivers installed and the game is up to date.
After all that is confirmed and there is still a FPS drop, try looking into the software you are running on your computer that may conflict with the game, for example, the firewall and antivirus. That is where the confliction of my games and the way they preformed was comming from.
Cheers,
ShrunkThatGUY
OP- What resolution and settings are you running? Also make sure Vsync is forced off in the Nvidia control panel. I also recommend using MSI afterburner to watch the FPS, and you can also monitor GPU usage with it too.
Personaly, I would've got the 7970 over the 680. The 7970 comes with 3GB(standard) ram, over $50 cheaper with the same performance as the 680. For you to get more then 2GB of ram on a 680, you have to spend $120-150 more then the 7970.
Considering a 670 easily beats a 7970 by 10-15%, thats an interesting statement.
A 680 is closer to 20% stronger than a 7970, the extra Vram doesn't mean much at all. 2gb is not a bottleneck at 1080p, it may be slightly if he's running 2560x1600 though but not many people are running more than 1080p.
I actually run 2560x1440 with a 660 Ti and have no problems running any games with most being maxxed out.