Can you use pc6400 memory instead of pc5300?

Yes, it will just run at the max speed that the motherboard supports. So if the motherboard specifies pc5300, you're going to be running the pc6400 memory which is faster than the 5300 at a lower speed. But it will work just as well as the pc5300. [thumbsuck] Might even run a bit cooler at the slower clockspeed due to higher quality etching for the pc6400 and or larger chip die sizes. [/thumbsuck]