its not a really a question of performance but budget what is best
I can get a 3gb 660ti for £260
I can get a 1.2gb 570 for £200
I am a gamer so what would be the best option? how much better is the performance of the 660ti?will it be noticeable in games?
At the other side of the coin I currently have a gtx 560 (non-ti) and it performs rather well would it be worth investing in a better cooler for it such as from the artic coolers, would this increase performance? and is it beneficial to have more vram
The 660ti draws far, far less power than the 570, and has a much higher texel rate. They have about equal memory bandwidth. The 570 does have a bit higher pixel rate but it shouldn't have too much of an effect as the texel rate is far more important.
Not to mention that 3GB 660ti model has double the memory of the 570. Just get a 2GB version, it will be cheaper and still great.