I don't have any firm numbers.
I don't believe you'll find anyone who really does..... at least nothing recent. Data from the 90's will be out there, but not really relevant now..... 25-30yrs is a long time....
That said, I believe that Chinese heat treating will be "on par" with the rest of the quality of the firearm.... some will be perfect, most will be Ok, the odd one will be done incorrectly....
If you're concerned about it, the cost of having a reciever annealed and then done correctly is fairly reasonable. Add up the cost of a NIB rifle + heat treating = less than a LRB reciever....
John