You better just get 16GB of memory. If you do anything heavy like video editing mine can crawl at 8GB. Plus I like having the memory for running parallels and virtual sessions.
You can no longer upgrade memory on Macbooks. They have changed this with the new design. The memory is soldered into the mainboard. Old Macbooks could swap the chips and upgrade. Whatever you buy, you are stuck with unless you buy a whole new Mac. Apple has decided to rape us.
Current Stable: Some Audi with a V10, Couple of BMW's, one F Car, and one P car. One lonely GT-R with all the Euros.