The effect of increased RAM can go only as far as the system can handle the RAM
, In case maximum capacity of RAM that your system can handle is 2GB and you gave installed 4GB in it, hoping to outperform, then that is not going to happen as 2GB of memory would lie wasted. Another consideration is the memory of the video or graphic card in your PC. The graphic card is capable of giving more depth and sharpness to images in PC. A faster and a powerful graphics memory would ensure that the performance is increased commendably. Once you are clear about your memory requirements, next step is to invest in reliable manufacturers for RAM, as they would deal with good quality RAM that would be able to give you adequate quantity of RAM as has been mentioned, and this would also ensure that no harm is done to your system too well.