As a Physics major I have to jump in here - not all of the energy used is turned into heat, in fact most isn't turned into heat at all. Heat is basically all of the wasted energy needed to run the computer. The rest of the wattage that isn't coming off as heat, the majority of the energy, is being used to do work. Basically flipping a bunch of transistors (switches) many times per second, spin hard drives and fans, etc. Heat is a waste byproduct of doing work in imperfect electrical circuits (ones with resistance, ie not a superconductor) - nothing more!
To the first question, yes it could be that it's a sign of inefficiency - but it could also be a sign that the mining software is not using the full potential of the cards.
You are right for all.
For who asked: transistors have very little resistance. Scientists and engineers study to minimize this, because it's a non-ideal phenomen that wastes energy.
Every year of development transistors in processors are more efficients and they have very very little resistance.
So, what is the reason because of heat? Count how many are the transistor in modern cpus and gpus
.
And now, why the gpu is more cooler with this gpu miner? Because lesser transitors are ON. So, GPU is not hashing at full potential.
I looked the OpenCL code of the miner. It works, but it's clear that it's not optimized.
To optimize it, it's not easy. At all. 11 differents SHA-3 algorithms... it's a long long challenge....
