Last summer, when I've installed my 4000+ X2, I've used Arctic Silver 5 paste, with a thermalright ultra 90. I've cleaned both the cooler and the cpu with isopropylic alcohol before applying the paste.
I've installed it first using the pea size drop, spreading it evenly onto the cpu with my finger covered with the plastic bag. Then I've installed the cooler and to my horror, full load temperature managed to hit 67 C with the chip clocked around 3 ghz. Took the heatsink out, washed it again with alcohol, reapplied thermal paste, but this time onto the heatsink surface as well as on the chip. My temperature reached only around 58 C, room temperature was 32-34 C.
When I got the cooler out after the first attempt, it looked like the paste didn't sticked at all to the heatsink so applying just a very tinny amount of paste onto it, improved the contact dramatically.