I'm thinking of buying this 4GB memory kit from OWC. It's two 2GB modules. But I don't know exactly how to figure out the optimum memory configuration when I install them. Should I install them on the same daughtercard as my stock 2x512 modules? Should they be installed in the same location as said modules, but on the other daughtercard? Should they replace the 512s? Should I even keep the 512s?? Confused!