Depending on what batch you have depends on how high you can go. The batch 1's I have goto 762 the batch 2's goto 662 and the batch 3's and 4's goto 737..

So far it don't seem to matter what firmware those are the levels I have made it to with my machines. I have 1 hashboard on the batch 2 that gets 1 x but it never loses speed. So I don't don't if this is a reporting error if there is actually something going on as long as I don't lose speed I don't worry about 1 or 2 x's

If you wish to try Efudd's when it is available you can try to set each board separately when I tried it didn't help any for my units but others have had different results.