I forget the technical side of things far too fast.
i believe double sides is 2 RAM banks, single sided is 1 RAM bank. double will run faster, although older motherboards might not accept it. Most DDR is double sided, cheaper brands aren't however.
so if hypethetically, and by hypethetically i mean actually, I had 2 sticks of doubble and one stuck of single 512 ram in my board, would that slow down my doubble ram so that my single ram could keep up, and would i be better off buying a new stick that was double and getting rid of the single??