Just looking for some insight, did some searching and didn't really find anything amazingly conclusive.

Does it actually make a big difference for engine temps?

 

I wouldn't think it would make too much of a difference. The entire engine is hot and the heat will eventually get to the rods no matter what is on them and become the same temperature as the engine. I don't see a coating on rods doing to much.

 

100% useless. The rods live in the crankcase and the highest surface temperature they should ever see will be oil temp, heat conductivity between the piston and the rod is not enough to be concerned with.