Just to add a bit more detail: 4GB of DDR3-1600 isn't NECESSARILY "faster" than 6GB of DDR3-1066. It really depends on your definition. If you mean clock speed, then it's trivially faster because 1600 MHz > 1066 MHz, but from a bandwidth standpoint, no, the DDR3-1600 is not "faster" because the 6GB of DDR3-1066 would be, presumably, configured in triple channel vs. dual channel, which would offer substantially more bandwidth. Not to mention that in RAM-intensive situations, faster RAM will NEVER make up for having MORE RAM - if that makes sense.
Also, I was incorrect earlier about the 16 exabytes - it's actually 2 exabytes. The limit is 2^64 bits (2 exabytes) not 2^64 bytes (16 exabytes). At that point, it doesn't really matter, but I thought I would correct myself out of principle.