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Lapping has no effect on it im afraid. It's the way the heatspreader is soldered to the cores. To be honest, Intel have COMPLETELY messed up the heatspreaders. Not only are they NEVER flat, they are more often than not incorrectly covering the cores, resulting in some being hotter than others. 10c is unacceptable really lol. Could be 20c, 30c, 40c, as long as it runs at stock, they don't care even if they say "bestest ovaclocka evar!11'