As far as I can remember(I've been out that OC game for a while), the difference between the two should be minute. Some do better at sub zero temps, some at idle etc.; it's all tailored to those type of extremes IMHO. While the conductivity differs between the two, ceramique being the safer for bleed-over on leads. I never really was able to get a decent spread of AS5 under my sinks. I used the recommended size for the surface area(half a grain of rice and tinting). But like prcguy said, a dabb will do you..and you already know how large a CPU is.
That said, more airflow has always been the route I've taken