hi im running 2x2gb of DDR3 ram at 1600mhz for a total of 4gb of ram i am wanting to know if it will be a good idea to install 2x2gb of DDR3 ram at 1333mhz will it just slow down my system or will the extra 4 gigs give me a boost in performance.
It depends on what you're doing - in most cases, it would speed up your system. Your OS will be able to cache more frequently-used components, and you won't need to swap pages to disk as frequently, etc.
For use cases where you're working with small data sets and memory bandwidth is the biggest performance bottleneck, it might slow things down a bit, but this is probably not typical for most users.
IF (the operative word here) the memory is compatible and will work together. There are so many variables (timings, brand, etc...) it most likely won't.
Theoretically you will get a performance boost just because you are using more RAM, but it will have to run at the slower RAM speed.
If you can swing the expense, buy a set of sticks in the about of GB that you need. Mixing and matching RAM doesn't usually end well.