I had posted this earlier.
You can try out some of the components listed there. And for gaming purpose, you'll need at least 8GB RAM and 1GB graphics card now-a-days.
Wrong @ RAM
For gaming,4 GB is more than enough.Those extra 4 will surely help you a bit,but while gaming a 4 GB 1600Mhz ram is what you need.
As per graphic card,2 GB is recommended for 1080p gaming as the memory (1 GB or 2) helps in rendering.So,if you have a 2 GB card and you try to run that game on 2560x resolution (Don't know exact one),the game will lag unless you lower down the graphic settings.For graphic cards theres a lot more to be seen. CUDA cores,clock speed,memory type and so on..