zrenix, i see the bigger chunk (512) is slower and the smaller chunk is faster. as a rule, you should use same speed ram in the same computer. this is because it will all be run at the speed of the slowest chunk. thus if you have a ddr2700 and a ddr2100 in the same box, all will run as if it were ddr2100.

(note that on some older/exotic mb\'s there might actually be an issue hanging the boot if you mix memory speeds)

if you can somehow manage a split so each computers gets equal speed rams, it will be perfect. if you dont, you lose some ram speed, but it shouldnt make (much) difference.