Better for gaming: Intel i5 or AMD Quad-Core A8-3820?

Your links are not working for me.

No game will use more than 2-3gb of ram by itself. 8gb is usual, but 4gb will still be ok.

A prebuilt is good if you like it just as it is, and it will not ever get any upgrades.

Once you start changing things our for gaming, you will do better assembling one yourself.

What is your budget?