Go
here and scan your memory. They extra money is not worthwile if the memory that you already have is slower. The new memory that you put into the system alongside the slower memory will simply slow down to match what you have.
If you are removing the memory that you have and putting in new memory then you want to make sure that the memory you are buying is actually correct for your motherboard.
This scan will tell you that.
If your motherboard will support the faster memory and you are taking out the old memory, then the performance boost may be worth it to you.
