You could checkout the Large Address Aware 4GB patch on nexus, my game was lagging when i started downloading mods, i thought i need a more RAM untill i found out about this Large Address Aware executable mod, it helps my game run a lot faster,
not sure if you already have this already:
https://www.youtube.com/watch?v=nzJze2d4QKU
Im using a quad core pc + Intel(R) core(TM) i7-3820 CPU @ 3.60GHz processor + GTX470 video card:
im also running the game with high quality texture packs + high settings blackout ENB, and my game runs very smooth with the help from the 4GB(NVSE) enabler.