I have always used the stick-on type of heat sinks that are commonly available for Rpi3. But from my electronics background I would use thermal paste and a very tight physical connection. So my question is in the title: How much difference do the stick-on heat sinks make?
There is a bit of difference between copper and the more usual aluminium but...
- The general ability of medium quality aluminium to conduct heat - 205-210 W(m K)
- The thermal tape used is at least as conductive as, or close to, the ali' heatsink
- The surface area of the (larger) heat sink ~2cmsq
it should be able to offset around 2-3deg. Not a lot but it's better than nothing.