The gtx560ti is a great card, and will definately meet your needs for high settings and 1440 x 900 resolutions in most newer games.
The only issue that you need to consider is the rest of your components and how they will perform with your new gpu. You seem to be only upgrading the gpu...which might be a mistake. Your current cpu was good back its time, but currently it will bottleneck your gtx560ti quite badly. The gtx560ti and Nvidia cards in general are more reliant on cpu power compared to radeon cards.
So you have some options here:
1. You should hold off the upgrade until you can atleast afford to get a new cpu and motherboard. This way you will be sure that you are getting every once of power out of all your new parts.
2. Buy the card now and upgrade the other parts later. While your cpu will bottleneck your gpu and quite heavily at that, it should still perform better than your current card. Given that your playing resolutions are not full hd and you plan to play games on high settings...this might be enough for you. I bolded might because it really is a gamble.
3. Get a radeon card. The radeon HD 6950 has been canceld as far as i know...but you should be able to get a 7870 or 7850 for a similar price and similar performance..not really sure on this. But it is an option. Radeon cards tend to be less reliant on the cpu.
My suggestion...hold off until you can afford a full upgrade, or atleast the core components (motherboard, cpu, and gpu). You dont need a hell of money to do this. So the wait shouldnt be too long!
The thing is someone who has a better cpu than you, say for example a new i5 cpu but has a significantly weaker gpu like the gtx550ti....could get better performance than your core 2 duo E8400 and gtx560ti combo!
Really since when? I bought mine six moths ago.