they are the same chip, except one has a higher clock. BUT if the chips are binned, the likelyhood of the max clock on the 8350 is likely to be higher than the 8320 on average. but if you come across a good 8320, then its exactly the same.
basically luck of the draw. the 8350 is just more likely to have a better chip, but doesnt necessarily mean that all 8320's are worse than it.