I’ve got my Slice CM3 rig running RasPlex down to 47° C from 68° C playing BlueRays or Dvds using 2 Standard heatsinks that are normally shipped with some Pi Cases. - The Blue ones
I’ve got one sitting on the CM3 and the other off-set on the lid so that they interlock.
Then I filled the space in between with Arctic-Silver Thermalpaste and then closed the Lid.
I then opened the rig again to check if the pieces fitted together.
All looked good. the two heatsinks fitted - interlocked - 1A and the spread from the paste was spot on.
Now every thing is spot on, Temps never above 52° C