typically you shouldn't change the speeds of the sticks you're using, expecially for ddr, instead stick with the 2700, and get a stick of 512, so you would have a stick of 256 and a stick of 512 correct? both at the speed of pc2700, i've just heard horror storries about using 2 sticks in dual chan, with 2 different speeds, but it's up to you most definatly... the size of the stick won't matter, the more the better, but speed can screw things up (maybe)