You shouldn't need to use overdrive for C2 at maximum settings with a 7970.
Yeah, when it was released it was a system pusher, but a 7970 should be able to run Crysis 3 at high settings with only a bit of effort. [Note I didn't say 'maxed out'.]
C2 is pretty old, and a 7970 3gb should be able to handle it easily without Overdrive. I'd be keeping my eye on CPUID to monitor the card. [It's a free DL, google it.] I'd also be planning to upgrade or replace the card if things don't improve.
You shouldn't be having difficulty running a game that old on a 7970 card. It should be running smooth as butter.
I've got three of them in xfire and I turn it off and disable overdrive if I'm running anything as old as C2 so I'm only using 1 card at stock settings. I get 60+ fps easily in C2 with no hickups at all.
If you've got it running, great, but I'd be keeping an eye on things. You seriously shouldn't be having any problem running Crysis 2 on a 7970 that isn't OCed at all. If you're having issues running a game that old on hardware that powerful, something is up.
Couldn't say what, but I'd be suspicious and start monitoring my system and planning ahead just in case I had to replace my card.