I am thinking of upgrading Graphics card in future and wondering if my i5 (3.1 Ghz) is enough to push a 4gb vram Graphics card TO THE LIMIT, and does it matter if i only own 6gb ram, do i need 8gb or 12gb ram ?
Depends on what the card is, which model of the i5 it is and what game and resolution you will be playing. Generally, an i5 will match well with any video card to run at high settings.