I found a few free RAM pieces that i wanted to add to my grandmothers laptop. She currently has 4gb ddr3 1600 running. Would adding 2GB ddr3 10600s 1333 help or will the lower overall speed hurt?
The faster RAM will clock down to 1333 Mhz. For whether it will hurt, consider the following:
1) More RAM is generally more useful when you are doing memory intensive operations, which I can hardly imagine your grandmother doing.
2) Faster RAM is always better.
3) That said, if you have some big applications that you will open and close repeatedly, then more RAM will make lots of difference, since you have more space for caching.
Finally, my opinion is to have more RAM under Windows, and faster RAM under Linux.