They would be close i guess. But the GTX 660 is based on a different card than the 760 which is why the 760 is more inline with the 670 because both the 760 and 670 use the GK-104 Chip while the 660 uses the GK-106 Chip. Ultimately its up to you to buy one. GTX 760 = Better Performance. GTX 660Ti = More Cuda Cores and 1GB More Ram on that model. Both are great cards for the price range.
Graphics Card RAM helps with pre-rendering of the graphics in game right now the sweet spot for ram on GPU'S is 2GB But i think in the future games will use more than that seeing as the next gen consoles will push gaming forward in general. The Extra 1GB would help but i think you should go with the 2GB 760 as it will be at least 2 years before games require more than 2GB of vRam.