Who told you that was a high end build?
Problem 1: ---I5--- It's just a new name for the word "Celeron"
Problem 2: Windows 7 64bit (home edition)
All windows 7 even pro 64, with exclusion to ultimate still has the 3.2gb memory limit (straight off Microsoft's Technical forum)
So you have 4.8gb just sitting there gathering heat only.
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What resolution are you running at?
The higher you go; the more memory gets taken away to run the game. (so if your at 3.2gb do the math)
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This games video rendering is pretty intense!
You video card comes in 3 versions 1gb 2gb an 4gb
Most Games have the option of hardware/software control.
(however) I'm beginning to wonder, that by default this game is 1/2 software then video controlled, (which would explain the heavy CPU usage).