You said your ssd only needed to be X in size +another 3GB.

SSD's. Whatever you think you need in storage size, double it.

My MBP had a 250 GB disk. And was more than half empty. I bought a 120GB SSD, then wound up buying a second one and putting it in place of the cd drive. I'd have been better off just buying the 250GB to start.

Edit: reread the top post. "OSX & Windows" definitely get the ~250GB SSD.