Forgot to add: it is better to spend your money on things you need, in this situation.
> 6GB RAM makes no sense.
Your graphics are not rendered into your RAM, again, unless specifically written to be so.
RAM stores program variables, structures, code, data of specific types and so on.
No modern game application uses more than 3GB of RAM, unless it has some issue in it where pointers, strings or the like are dynamically allocated or converted wrongly, causing memory to constantly rise (i.e., overflow of data in buffers).
You'd do fine with 4GB, 16GB you won't ever need for playing modern games.