Difference in core temps

I'm running an E6600 with liquid cooling and Arctic Ceramique, and a 4-5 degree difference between my cores at idle, and 6-7 degrees difference load, and I'm just wondering if that's normal or if my thermal material got skewed to one side when I applied it. Also, I was wondering if I were to reapply thermal material, should I stick with the ceramique or get some Arctic Silver 5 from a buddy of mine?

Thanks for the help.