Better binned is the right word. And $178 Sounds about the right. New gpu at higher price than the old one... that is the direction of gpu prices... but $178 is less than the release price of 580and considering the inflation the prices Are actually redusing, but the pace is not very quick in that aspect.
Most likely is just a small chip, there Are less actuall defective chips, so the binning is the way of making different product segments.
But untill official release we can not be sure. It is suposed that Apple gets all 24 core parts and retailers gets 22 core parts (binned at different speeds) and 5300 is even more cut down version this time...
I would Expect some ram speed differences Also between the Xt and non-Xt versions, but that is just my personal ques. But the above is based on ”leaked” information about the product. We have seen false product info leaks before, but nobody else than Apple seems to have any hints of having 24 core parts, and that makes some Sense. The problem with that info is, what amd could call the 24 core version, when Apple don`t need all of those chips? 5505? Or 5500xt+... all in all that time if far in future, but it will come eventually.