I'm sitting at 33 C idle, doesn't go much above 40 C under load. Heatsink is a slk-800(a) which has very similar results. Everything running stock, 80mm panaflo fan. Sys temp is 31 C, case is 27 C with 3 intake fans and a 120mm fan in the back and 80mm fan blowhole. (room temp around 74 F)
Better case cooling would help but that doesn't explain the 20 degree difference between sys and cpu temp. Unless you have the fan backwards or dumped a ton of AS grease on it, it sounds like the mobo may be reading temps high. What software are you using, MBM, Asus thing, or just the bios temps? I've heard of major differences between the Asus software temps and bios/MBM.
I didn't find the need to use the 4 extra HSF pads, may they're keeping the HS from mounting tight? (just brainstorming....)