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You'll find answers to this and many other commonly asked questions under the Guides tab at the top of this page:

If you have questions that these sources doesn't cover, you can check to see if it has been answered in another thread by doing a Google search of the forums to find threads like these. I hope this helps!
 
Very negligible performance difference. I ended up buying Mac-specific 2x2GB Corsair CL4 modules for my MBP, but it was on sale at Fry's at the time so I got both sticks for like $90.
 
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