Which the performance difference between copper and aluminum
 

Compensates to pay the double of the price for a copper waterblock.
Thank you.

Though the Z3 doesn't seem very popular here, a graph comparing its copper vs. aluminum versions (in addition to the copper with peltier) here

Usually theres only a small difference between a copper block and a aluminum one, but 3-4 degrees is a lot whem you think about it to some. If you just want a quiet system, maybe AL is ok for you, but once you spend on everything else copper is usualy only 10.00 more. If you change your mind later it'll cost you more!

The best blocks only come in copper also. Try a Danger Den Maze 2, there 42.00, but once you figure that you'll spend 10.00 for a decent holddown on a cheap block (or more), it's really not that bad (as it's built in!).