I want to add more memory to my Dell Dimension 3000. Currently has 256 Meg with one open slot.Uses 184 pin DDR DIMM modules. Mfr says to add memory in matched pairs. It says you can mix modules such as one 256 and one 512 but performance will be reduced. So, does that mean that mixing them will give you less performance than just one 512? Or that I will get more than 512 but not as much as 768? I would call Dell tech support, but we all know how good that is. I'm sure there's more knowledge here than at Dell.