Passive cooling, aluminium or copper?

Got an old socket7 im using as a 100% silent computer but of course the cpu's get a little hot! I wanna get a more appropriate passive (no fans) cooler, im looking at the zalman cnps 6000 alcu and cu. I know that copper conducts heat twice as fast as aluminium but it also has a harder time expelling the heat , but i dont know how much by and how it would work out in a passive system.

so alu or cu, and if there's something better than the zalman let me know. :D

Unless the computer is crashing why bother getting a new HS? you may as well just turn the heating off in your room and let the computer heat it up.