i would go for 6 or 8gb ram because its a fast spec quad core processor.
However you would have to be playing the best games or graphics designer software to use it. Note, online games, even though its an internet program, requires good ram and processing to run the game. the internet data is in code, and needs to be processed by your computer to send back to the internet game. So a fast computer will out shoot a gamer on a slower computer if their skills were the same. So this means you need a fast ethernet card. google fast ethernet card
You need to set a goal on what game you trying to run.
A see through case full of lights is lousy in a bedroom.
Biggest and best is big on electricity, like having ALL the lights on in your house, expect big electricity bills.
Biggest and best is a lot of heat = lots of fan noise - like sitting in a factory, consider water cool.
Two screens lot of fun, consider a video card that will drive two screens.
Ensure your graphics card will run on win7 etc. Some cards require vista.
play with this on your existing computer and compare the specs on the new computer
Can this computer run that game?
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Run this program and click the red "We Recommend" where appropriate.
http://www.systemrequirementslab.com/cyri
Note Halo2 is demanding on the operating system, see what it recommends
Crysis Warhead is demanding on the video card, see what it recommends.
Far Cry and FEAR is demanding on the processor.
WOW is a general all rounder, not as demanding as above.
When you see the Pass result at the top, look carefully as it shows the minimum to the best performance for that game., even though it pass, it may not be enough for maximum settings., so check the resultant Green chart ruler line at the top.
Click the Red fail tab as well.
compare the specs to what you going to buy. The above is a bit old, choose power hungry games if you know of any.