I also use water cooling and have the i7-3930k and I have found that the Sandy Bridge-E processor does run a little hotter then the other processors, I got very similar temps before overclocking my cpu. Right now when using real temp the temps are in constant motion so I have the min. and the max. that I can post and that's with just open web pages so it's pretty close to idle. But it is overclocked to 4.5ghz.
min. C1-42 C2-39 C3-37 C4-33 C5-40 C6-37
max. C1-54 C2-52 C3-49 C4-48 C5-51 C6-50
You only posted four core temps and your processor is a six core, did you leave the other two cores out for any reason? The idle temps that you posted are fine as I said this processor will run a little hotter then the regular Sandy Bridge because it has a higher TDP.
Ivy Bridge --77w
Sandy Bridge --95w
Sandy Bridge-E --130w