Im curious to see what the larger z9 can be overclocked to and if they use the same chips as in these. Perhaps you're right maybe they picked the best ones for the z9 and used the rejects for the mini's.

I did have one mini from the first batch which has the same chip issue. I could only overclock to 550m before the middle board would drop out. My other first batch ones are all stable at 750.

So far my second batch ones are running stable at 675m for 10+ hours and getting 14-15 ksol which isn't too bad.