Sorry 1 - My US/English is not my native language so maybe I miss something in your topic !
I am speaking only about the fact that with 64 bits Software on 64 Bits Windows
you don't need to set any parameter to be able to use all/more memory
I don't speak about hard disk, fragmentation, etc ...
Sorry 2 - As Antonio said, I have forgotten something : increase the swap file size !
With 8 Gb memory, my advice will be : 16 Gb to 32 Gb for the swap file size !