Hi, I'm thinking of getting a base rMBP 15, and was wondering whether there is a chance that the 256GB will have worse performance than the 512GB version? I know the 128GB SSDs in the MBA are somewhat slower, and was wondering whether the same applies to the 256 & 512 SSDs. Also, does Apple use both Samsung & other brands in the 256GB? I had heard that they only use Samsung in the 512GB & 1TB, and that the Samsung SSD are considerably better (and faster) than other brands. Any ideas? Thanks!