From your specs and model size you should not have memory issue unless you are using grahics vs what you noted with large memory or maybe dual monitors. Their memory gets subtraced from what you can use because w7 till maintains compatibility with x32 that cannot use extended memory address space above the 4gb limit
Chack the two items of page two on this link especially the one about unchecking max memory use http://www.sevenforums.com/hardware-devices/5816-windows-7-64-bit-ram-issue-2.html
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