If the cpu is not overclocked and your using the Corsair H-100 I would want the idle temp to be lower than that , somewhere in the 30's. The reason being is that if you overclock what will your temps be if they are at 43c now.
I have water cooing and the H-100 is similar to the radiator that's used in water cooling , I have the Intel 980x cpu which is a six core and my temps are in the 30's. So what did you use for thermal compound or was it preapplied? Do you have the two fans pushing or pulling air through the radiator. If your trying to figure out if you set up the H-100 right or wrong , How is it set up now?
I am using a Single 120mm All in one cooling solution from Asetek and my Idle is 27 C. I am using the Silver stone FM121 120mm fans in push/pull configuration. At full load with prime95 running, My max temps are 57 C.