Hypthertically speaking if you used no more than 2GB it is unlikey they are not an intense gamer or into overclocking as a result so out of the 4GB and 8GB options I would just go with the cheapest, any more would be just "head room".
I would however advocate more memory if the speed offset was only the difference of 1333 and 1600Mhz just as The Great Randini has prompted.
sorry for the above reply,ignore it. I told that I won't be using anything more than 2GB. So what is the need for that extra 6GB of RAM? Will it improve performance? How?
Unless you only plan on using your computer for Microsoft Office or Minesweeper or something like casual internet browsing you will use more than 2 GBs of RAM. If you need more than that, it will improve performance. If you have more than you will ever need, it won't make your computer any faster.
That's why it's recommended to get 8 GB as it's the sweet spot.
Faster RAM is great if all you care about are benchmark scores. You are not really going to be able to tell difference in everyday usage.
However, if you are talking about playing games with an AMD Llano APU and you are relying on the integrate graphics core, then faster RAM will improve gaming performance. That is because integrated graphics relies on the system RAM.
However, the integrated graphics core in the Core i3/i5/i7 does not seem to get much of a performance boost from faster RAM.