I played heavily modded Oblivion for the better part of 6 months. Then I got bored and switched to heavily modded Skyrim. Then I got bored again, so switched back to Assassin's Creed 3 for a few months, and now I'm back on Guild Wars 2, which I've had since it came out.
There is exactly no telling when I'll be bored again, it'll just happen, (already starting I think) and I'll get something like TitanFall or the new StarWars.
You play your games now, and a gtx960 will work great, but what happens when you get bored of them and switch to something a lot more graphically demanding. Considering the price of the gtx960, and then the price of its bigger brother the gtx970, it would be worth the time invested in saving more. It's not exactly future proofing as much as making allowances for your future decisions.