I have a xps 420 5.5GB ram, quad core q6600, gtx 660. I plan to upgrade to a msi z77A-g45 Thunbmderbolt with an i5-3570k, h110i, xion gamin case, 1000w psu, and keep my 660 ti 3GB and Samsung SSD. My question is why should i upgrade to this new computer if my xps 420 still works fine.