GPU Upgrade; 770?

[NeverWinter]

System specs:
i5-3570K
Z77X-D3H
16GB Patriot Viper
GTX 570 1280MB
1920*1200

So I could get either another 570, a 680 or a 770. I could dip in to the 7970 but I think I'd miss the physx...

My system is all currently stock but I'll look to OC everything at some point.

Any other ideas?

 

[NeverWinter]

I'm looking to spend £300+

What's the reason for picking the 680 over the 770?

 

[NeverWinter]

I've purchased myself a Palit GTX 770 JetStream 2GB, should receive it tomorrow managed to get it for £310.