This is for a macbook, but it will give you some idea of 2GB vs. 3GB on integrated graphics:
http://eshop.macsales.com/Reviews/MacBook/Testing/Memory_Benchmarks
I thought a MB could only handle up to 2GB ram? From what I understand putting 3GB in would be a waste of money because about 700mb or so of that 3rd GB won't ever be utilised.