Francisco Costa :
The FX-8320, it's an underclocked 8350, but much cheaper. Then overclock it to 8350 speeds and you get an 8350 for the price of an 8320. Profit.
normally this is true, but you can never be sure that the 8320 will work properly at 8350 speeds. yes, it's the exact same architecture and there's no reason for it not to work, but you're at the mercy of the binning process at amd.
it's possible also that you get a 8320 that will not be stable at the 8350 speeds no matter what you do and that's why it didn't get binned as 8350.
the 8350 is the safe choice, since it passed factory testing at those speeds.