Hi, i have an Intel Quad Core Q6600 2.4 GHZ (stock), and i changed out the dell heatsink to an zalman heatsink. I used all the parts except the square looking mouting bracket that goes underneath the motherboard as my stock one held the screws fine. Also i got the artc silver thermal paste.
I have the same processor, only a different aftermarket heatsink and fan. I have mine pushed to 3.2 Ghz and my processor temps read at the following.
Core 0 = 47
Core 1 = 46
Core 2 = 39
Core 3 = 42
My temps will be a little more skewed than yours just because I am far over the stock speed. However, core 2 (your core 3) is the oddball of the bunch. I don't think there is any problem with the temperature being different than the others. I have been running my Q6600 chip anywhere from 2.8 to 3.2 Ghz over the past 6 months and I have never had a crash because of the cpu. I don't think there is anything to worry about.