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I'm not sure about COD, but BF4 multiplayer can get quite CPU intensive. So one of those Pentium K will bottleneck a 970, the 760 may be ok due to it being a less powerful card.
The good thing about those Pentium Ks is that with the right motherboard they offer a good upgrade path to a 4770K / 4790K
Yeah a second hand i5 / i7 would be a good move.
Are you wanting it for the setup in your sig or is a different computer?