My pc specs are core 2 quad q6600 o/c ed to 3ghz. 4x2 1333mhz kingston rams .Gtx 660 oem..i cannot play WD in ultra preset using 1360x768 resolution..sometimes it lags heavily. i had set the textures to medium when driving it still lags but walking is just fine. how can i improve gaming quality without lagging?