I wouldn't be too worried about the differences between batch 8 and 10. I doubt that they would be releasing a later batch that is less stable. I think the main reason they have them separated out into two different products is because of the difference in pricing. All of the specifications of the S7 are exactly the same - you're just paying for an earlier place in line if you buy batch 8.
I think it is the difference in pricing. The price is getting cheaper lately as they are not as profitable as before.
I think that is the only difference I think batch 8 and up are all the same design. The big thing is the design has less chips, which means less cost or should at least. They managed to do less chips and higher frequency. This allows them to sell for cheaper one would guess.
And difficulty is crazy right now so price will change likely a lot of this continues.