they are linked. copper is a good conductor of heat, but like all metals, a poor insulator. touch a hot water pipe made of copper and then a pex pipe and you can feel the difference. the loss of efficiency comes at lower temperatures (such as idle or system startup) when ambient temps are high (such as summertime or being near a source of sunlight). the copper could be warmer and heat up the components faster. the loss would be minor, if at all noticeable. it's more of a theoretical loss on paper than anything. under load, the copper could actually help dissipate more heat provided you have strong chassis fans moving air through the case. in the same breath however, the copper lines inside the case will be hotter than regular tubing and could potentially heat up other components. generally speaking, there isn't a performance hit taken when copper pipe is used but it is far more difficult a material to work with.