As for temperature sensitivity, as you describe it, I see that also. The core temps are very mobile, even under small loads - I think it is pretty normal. If opening a program or two has the temp jumping a bit, but it recovers right away, this is also nothing to be concerned about.
Remember, your over clock listed in an earlier post is on the order of 50% - that is very high, so it is not surprising that there is movement on the temps. The primary concern should be where the temps top out under load - that is where a higher performance cooler usually shines, and honestly, where it matters most for system stability and long term component life.
I did finally pull my Xigmatech, and the spread was pretty even, though a bit thick. I redid it, using a little less and more along the methods discussed above. Temps did not change at all in my case, but they have been quite good already.
The base of the sink is a little rough, but no more than any others I've used, and less than some. I think careful TIM application is important for this sink mainly to avoid making a mess, which I did to some extent. I'm glad I reapplied it even if my temps are the same - at least I know it is done correctly.
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