Is a sandy bridge better, clock for clock? Yes. Is it worth buying over an i7 950? No.
Be honest here, have you ever thought your CPU just wasn't adequete? Gaming wise, the difference will not be noticeable. Neither CPU will bottleneck any GPU set up. Although I'm pretty sure the X58 still has more PCIe lanes than the P67, so feature wise you'd be downgrading.
But yeah basically it's a waste of cash. I mean, if you're looking for specific performance increase in one area or another you can just upgrade the GPU (if you need more FPS) or buy a 970/980X CPU if you need more performance that way for some reason. Or for a cheaper alternative, overclock.