Emailed my teacher asking for direct grade boundary predictions. His response-
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"Hi,
That's a good question, and not one I can easily answer at all!
I have only looked in detail at the Pure papers, and thought they were reasonable, in terms of level of difficulty, but time-consuming (I spoke to one of your classmates on Friday, who I'd expect to get an A*, but they didn't finish).
I am used to (roughly) 90% for an A*, and 80% for an A (those are the only boundaries you need to be concerned with) - I cannot believe they'll be that high this summer, but can't predict with confidence what they'll be.
How do you think you got on? Please try not to worry over the summer."
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Make of that what you will, though all I make of it is A* < 270 and A < 240