It will depend on your motherboard how the memory is used and you should check the manual to see which slots to use for triple channel. If triple channel isn't supported then it should work fine as a double channel and single and increase the overall performance of the system and still be able to be overclocked as normal.
I forgot to post the motherboard, and of course it make sense knowing if my motherboard supports triple channel.
The board is an ASUS P5E3 "BASIC" (no deluxe, premium, etc). How can I see if it supports 3-channel? For sure the board doesn't support because it is a basic version, but whatever.
Since you said that "If triple channel isn't supported then it should work fine as a double channel and single and increase the overall performance of the system and still be able to be overclocked as normal", that means that I can use the 2x2GB modules as a double-channel and at same time another module of 2GB as a single-channel? My doubt is if it's possible to use both "operating modes" double-channel and single-channel at same time, and not only or double-channel, or single channel.
Ok, it's a little flakey at this point. Your motherboard is specced as having 2x dual channel only, therefor the motherboard will more than likely interpret 3 sticks of RAM as 2 dual channels, 1 with 2 sticks and the other with 1 stick. However it is not a recommended configuration in the manual and may result in an overall lower memory clock speed. It's a bit difficult to say which will be better, my general rule of thumb is 4gb to 6gb will be better than a lower clock speed. Since you have the memory already my advise is just to give it a test and benchmark to see which gives the better performance.
Right, the performance increase will come from doubling up the memory, the bandwidth of the memory stays the same as quad channel isn't supported by your mobo. There won't be any additional problems with overclocking due to the increase.