I think grade predictions are almost impossible. I was one of the ones to try on this group and wish I hadn't.
At the time DD was of the 'failed them all' mindset. After a week of reflection and looking at last years grade boundaries she's back to the 'I think I probably got an A/7 in everything except maths which will be a 6'. Don't suppose you remember but maths was the one she was physically sick in twice!
Even though she logically knew that you didn't need to get 90% in all your papers at the time all that was in her head were the answers she wasn't sure of. She laughed out loud when I told her the answer to the last questions on the maths paper was supposedly zero because that's what she got and didn't think the answer zero could possibly be correct 
Fast forward to the night before results day and she will be predicting 4s and 5s again.
The human brain is a funny old thing!!!
I am going to try REALLY hard not to start thinking about it until mid August.
Have you all done post exam autopsies with your DC yet or have they already 'moved on'?