I've been running Kingston HyperX 240-Pin DDR2 675 (PC2 5400) Dual Channel SDRAM for over a year now. I just realised that it is only running in Single Channel mode. I'm pretty sure it's because my mobo Foxconn 915A01-P-8EKRS only supports Dual Channel with a bandwith of up to 533 (PC2 4200). My question is, if I purchase the 533 version will I be able to run the new pair with Dual Channel while running the old pair with Single Channel? (I know that the old pair will probably jump down to 533 also.) Also, do you think it would be worth it for $100? Is there a noticeable difference? Thanks for the help.