I think either 50% or 100% is misleading without more information. In either case you can be left wondering where your bottleneck might be and your first guess probably is not something like more cooling.
I think showing 100% is far worse, because then I have to rely on my subjective experience of the interface I'm working with to notice that something is wrong. 100% isn't just misleading, it's wrong on a UX level. At least when it shows 50%, I immediately have a sense of, "wait, that's wrong" and I can even begin troubleshooting and look at the current clockspeed, temperature, core usage, etc.