The 560 Ti, is much more expensive, uses more power, and is outdated. Your CPU is going to bottle neck it any way. Yes it will perform better but not enough to justify the extra cost.
No perhaps not, but like I said with your CPU isn't great (it's about the same as mine) anything above a 650 Ti, will be bottle necked.
If you want to upgrade your CPU I'd recommend an I5 3570, or a cheaper I3 if you can't afford it. But then you'll need a new board, and probably a new windows license to go with it.
The 560 Ti, is much more expensive, uses more power, and is outdated. Your CPU is going to bottle neck it any way. Yes it will perform better but not enough to justify the extra cost.
Ok thanks Do you think ill be able to play BF3 on ultra settings or atelast high, with min 30 fps, with my pc + 560 ti or 6870 ? Talking about multiplayer
Yes, the 550 Ti isn't a bad card, but it was never a really great for the price (there was always something better for just a few dollars more was it's downfall). http://www.anandtech.com/bench/Product/541?vs=680