Personally I think it may be the quality of the thermal paste, I did a bit of research (i know i should have done it before I replaced the thermal paste) and found out the stock thermal paste on the vapor x is already pretty good quality so now what I have to do is to buy some good quality thermal paste.
EDIT: Yeah okay I am pretty sure its the thermal paste this stuff says 1,93 W/mK on it. Whereas the mx4 for example says 8,5 W/mK I am ordering it now.