Maybe that is it...
That clock speed at the top is the only part of the skin that is using all the clocks; as I mentioned above, it is the maximum of all the clocks. If you want to see the actual measure using all these values, in the CpuMain.inc file, the measure is .
You can certainly configure only a single core for this if you want, but your clock speed probably won't be correct. If you look at HWiNFO, you'll most likely see the clocks bouncing all around. They vary wildly on my machine, from <1GHz to nearly 5GHz, and not all cores on hybrid CPUs run at the same base clock. Your older desktop CPU might not show such wild variation from one second to the next like newer laptop CPUs.
You can map the Core 0 clock to HWiNFO's average clock value as an alternative. Whatever you prefer is fine, you can configure things however you like.