Gtx 645 Vs 750

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Not worth it, but not because of performance difference. AMD is releasing their new Polaris cards soon, the Rx 460 (~100$), the Rx 470 (~150$), and Rx 480 (~200$) which will be significantly more powerful than any other graphics cards available at those prices currently. Even the Rx 460 should be capable of running any modern game at decent framerates (assuming your CPU doesn't create a bottleneck in some games).
Not worth it, but not because of performance difference. AMD is releasing their new Polaris cards soon, the Rx 460 (~100$), the Rx 470 (~150$), and Rx 480 (~200$) which will be significantly more powerful than any other graphics cards available at those prices currently. Even the Rx 460 should be capable of running any modern game at decent framerates (assuming your CPU doesn't create a bottleneck in some games).
 
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