I have a motherboard that supports PC2700 DDR Ram. I have 1 pair of matching 512 MB sticks in there for a total of 1 gig, but I also have an extra 256MB stick that just came out of another computer. It is a single stick -- not paired. Should I add this third stick to my system to increase the total memory, or will this slow it down b/c of the DDR technology? Please explain.