Found a deal on 8gb PC3-10600 1333MHZ SO Kit (2x4gb) sticks. Question is, I have a macbook 6.1 the gf has a 7.1. Currently both our macs to my understanding have 2x1gb for a total of 2GB PC3-8500. Compatibility these sticks should work in either machine? Just they will be slowed down to our speeds of 1066mhz? Any cons if I take these two 4gb sticks, and I take one and give her one. Basically I would run 5gb total (1x4gb + 1x1gb sticks). Or would I be better off running just 4gb?