Switch over and take note of your temps, problem solved. 2xIR is already 720p, which is pretty damn decent performance, the 720 should allow you to reach 3xIR in a few games but that's as good as it gets, there isn't too large of a performance difference between both. Since you said everything going past 2xIR results in a slowdown it's safe to say that the GPU bottlenecks the CPU at that, the 720 should allow you to reach 3xIR and maintain decent framerates on a number of games.
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