Correct me if I am wrong, but isnt 3.8Ghz the boost clock of the 3570k? So 3.8Ghz is correct.
As you have considerable load the CPU has boosted its self.
Task manager does not take well to the CPU changing clocks. The CPU will report a 0.4Ghz boost and report it running at 3.8Ghz, then windows applies that extra 0.4Ghz on top of that.