Hi Sun --
Shaders, no, but you can adjust core clocks/speeds, right? That's accomplishing the same thing, if you recall the direct 2:1 relationship.
Remember also that a 660ti is essentially nothing more than a factory overclocked 660. You may not have much headroom, they may have cranked 'er good already. I doubt it, they're usually somewhat conservative, but just something to keep in mind. Example: I got my 465's from 1215 up to 1508. My 550ti, otoh, would only go from 1962 to 2054. Big difference. See what Galaxy 660's normally start at and you'll see how much the ti's been cranked already before it even met you. 
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