One of them not having "PC2" is most likely a typo or lazy product naming, and going by your computer's CPU socket, it is impossible that you use anything than DDR2 RAM. Most manufacturers and stores use "PC2" for DDR2, "PC3" for DDR3 RAM, or just "PC" for DDR1.

While it would probably be possible to make DDR1 or DDR3 RAM that has 6400 MB/s bandwidth (800 MHz), it is never going to be something you'll find in stores these days.