I have a 2009 MBP and a 2013 MBA. Both have SSD's and 4GB of RAM. The CPU is obviously different: a C2D in my MBP vs. i5 on the MBA. Yosemite runs buttery smooth on the MBA but is slow, laggy and choppy on the MBP. Will upgrading the RAM to 8GB make it better though? I don't want to spend the money and find out it's still junk.