That's true for HDDs because they top out before they get anywhere near SATA 2 bottleneck but for SSDs, SATA 3 can make a difference. Remains to be seen in benchmarks how much exactly.
You won't see any real difference going from sata2 to 3 though
There's a Samsung 4TB SSD if you can pony up €1200. ;)
So are you still limited to a 2TB hdd unless you use the ugly ass Nyko thing?