XPS Gen 5 memory

​ I want to add an additional 1 Gig of memory to my system. I bought the system with 1 gig of 667 memory. I called tech support and they told me I have 667 PC 4300 memory installed. I can only find 667 PC5300 or PC5400 to buy. Do I need to match the memory for the system to operate properly? ​

​ ​

​ Thanks for the help. ​