I have 4 x 512 MB DDR2, PC2-4200, 533MHz, CL4 RAM in my PC. My motherboard supports DDR2 667 RAM. I was thinking of buying (a) 2x 1GB Kit, DDR2-667MHz, CL5 or (b) 4x512GB DDR2-667MHz, CL5. Would I get a better performance from such an arrangement? In what slots do I put the 2x 1GB Kit? Thanks for an...