cas123

Upgrade or new system?
IF UPGRADE, save the money and get the 640. For normal use L3 cache don't matter that much.
or If you are feeling lucky and have MB that support ACC then 555 and try to unlock the 3rd and/or 4th core. Does not work all the time so try at your own risk.

IF NEW SYSTEM, get Intel i3 2100, around the same price of 555 but much faster.