I can't comment on the difference...I never inquired about the aluminum block when I bought mine (Cu)...we did talk about battery effect, but that was it.
Come to think of it though, here's a guy that has a few systems running on one water loop...one being a dually, and he's using his copper blocks on them.
IMO, he wouldn't use 2nd best (and more expensive) when he has both at his disposal. Would he?
