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It's a GK106 GPU minus an SMX, a GPC, a memory channel, and 8 ROPs. It's thus anywhere between 2/3 and 3/5 of a GeForce GTX 660, depending on what hardware you're looking at. It also loses GPU turbo and some clock speed. Unfortunately, they're starting with a card that is heavily constrained on memory bandwidth (and possibly ROPs) and taking away 1/3 of each, so performance hovers around 2/3 of a GTX 660--and sometimes comes in below that, even.
Even so, don't be fooled by the name. The GeForce GTX 650 Ti has nothing to do with the disastrous GeForce GTX 550 Ti or GeForce GTX 650 cards. Or rather, the others weren't really bad cards, but they were substantially overpriced for their entire lifetimes to the degree that they only reasons to consider one were Nvidia fanboydom or cluelessness.
In contrast, the GeForce GTX 650 Ti is a decent value at its MSRP of $150. Well, assuming you can find one at $150; on New Egg, they start at $155 and go up from there. It's faster than a Radeon HD 7770 at nearly everything, and often by a lot. Meanwhile, it's slower than a Radeon HD 7850 at just about everything, and again, often by a lot. Not coincidentally, it's priced between its two nearest competitors.
There are both 1 GB and 2 GB versions of the card. No mismatched memory channels for marketing reasons this time, so the stated amount of video memory is what you get. While the world is shifting toward 2 GB cards (high resolution textures seem to be pushing that shift), if you genuinely need 2 GB, you likely have the budget for a higher end card.