I can't tell what each of those are......
The difference between 'normal' grade thermal pastes generally result in a degree or two swing (either way). Some of the higher end stuff can do a bit better. Even then, generally, it only really shows at higher voltages.
Given you can only BCLCK OC the 8400, the increased voltage aspect is not likely to be a huge factor. So I wouldn't bother.
I doubt you're going to see more than maybe 1-2'C improvement and, depending on the quality of the paste/application, could actually see higher temps.