The all Cu does work better but it is much heavier. There exist chip/board maxium masses for heatsinks. The AlCu comes just under the max mass for an A64s as I remember. The Cu being heavier, would exced the max mass. I mounted a Zalman 7000A AlCu on my A64 and lanparty nf3 250. Only complaint I had, sides the hot boot temp ( havent resolved this issue yet ), is the cr@ppy backplate. This cooler is suppose to be good, hope I figure my prob out.
edit wrong month and day...im so 'special'