I don't know what thermal compound comes stock on your heatsink.
For overclocking, it's better to use a good thermal interface compound, which really helps reduce temperatures, especially when under load.
The standby is Arctic Silver 5. That's what I use.
I've read where some people say Arctic Ceramique is as good or even better than AS5, I don't personally know.
There's another one called Shin Eitsu, supposed to be good too, I don't have experience with that one.
You can put it between the cpu and its heatsink, and also between the chipset and its cooler. Will bring under-load temps down several deg C.