The switching in cpu frequency is because your power plan is probably at balanced. then the cpu give more power whenever it needs it. Mine does exactly the same thing here. that being said your idle temperature is higher then mine but i use intel extreme tuning utility to lower my voltages for the cpu and i repasted my cpu here so my idle temps are round 40 degrees celsius. try that intel XTU and lower your voltages and see if the idle temps drop. the settings i chenged are dynamic cpu voltage offset to -68,35 mV and processor cache voltage offset -68,35mV. also i increased the multpliers here: 1 active core 36x, 2active cores 35x, 3 and 4 active cores both at 34x.
Hope this helps