Powercolor's won't cool the card as well [and isn't as good of a manufacturer], but aside from heat, will perform similarly. You shouldn't reach the performance throttle point of heat with either though. However, if you plan to OC, that will be a factor.
But, to give you a short answer, the Sapphire is the better of the two
you are over thinking it man. The brand discussion is pedantic at best. just get whatever one is the best priced at the time. radeon is going to be cheaper right now especially for used as mining is no longer profitable. nvidia is more expensive but it does have much better drivers and physx. you get what you pay for.