Out of preference, I would use some third-party stuff ... Arctic Silver 5 is what I have on mine. It's not hideously expensive, but I'd recommend picking up some Isopropyl Alcohol and some coffee filters (cheap lint-free cloths!!) - to clean the existing stuff off the heatsink before you apply the new stuff - in addition to just the thermal compound, as you need to make sure you get a nice clean surface to apply it to.
The difference would probably be only a few degrees, but if a job's worth doing ...
