Well I have a couple of questions to kind of point you in the right direction.
What is your current setup
And what games do you intend to play? Some games use Physx that's why I ask in most cases this wont effect the games you are playing but if you play games like Batman AA or AC, or even borderlands 2 you may care a bit more because it will change the feel of the game.
Also the 660ti is regarded as too expensive for what it is and people will suggest the 7850 or the 7950 as better alternatives.
According to that, the 660ti and 7870 produce very similar framerates in most games. Since the GPU's are produced by the different companies using different architectures the comparisons between the clocks, fill rates, shaders and texture units is not a 1:1 comparison. The only way to compare them is based on their performance in the games and applications that you are using. The webpage you linked only compares the specs not the actual performance.
Its better to match a card to your system. Like Bigshootr8 asked for the cpu, mb and ram should be listed so we can recommend the best card for you, also a power supply would be good to have. Most played games or games your wanting to get and the resolution that you game at.
If your getting close to $300, I would recommend the 7950 but at $255 I could argue that the 7850 is a better deal. Now if you find a 7950 with rebates down to about $280 then for me it would swing back into favor.
Np. ill try to always list my components in the future.
$250 or less sounds the best to me. bbbut i have to keep in mind, my comp is probably a pos. and ill probably be upgrading in the future, but id like to take with me these new items im buying (power supply and video card)
so with that said, ill go the 250-300 range... but only if its WELL worth the difference.
so its a no, for the 660ti. and go for the 7870 or the 7950?
I guess my only question would be with his current CPU would he see bottle-necking. But if you are getting a new video card and a new power supply I suppose its not a bad idea. MY rule of thumb is get what you can afford. If you have no intent in the future to get a SLi/ or CF setup I would get a 600/700watt psu like these. I would say yes the 7870 and the 7950 will give you more performance at that price point unless you are set on physx on nvidia brand name titles its better to go with the AMD solution.
If your wanting to stick with AMD look for a good AM3+ mb. They have said that until they go to 22nm they are going to stick with AM3+, so that means the next 2 generations and the 2 current gens, you could use the same MB and processor.
Your processor will bottleneck both of those video cards, however if your looking at the future, I would go with the 7950. The potential for longer lasting video card. Like I posted, I'm not looking to upgrade from the 7950 anytime soon. I'm aiming for 3-4 years out of the card.
Video cards when overclocked to that extent tend to shorten the life of the video card. How I look at this is, I buy the 7950 which is a bit higher in price, ~$60, plays everything on full now(maybe not with your processor but you did say your looking to upgrade that also). When it starts to show its age, over clock it a bit and run wild for the next 1-2 years after that.