Actually I have a very strong prediction for computing. My computing teacher was a ex-OCR Examiner/Moderator. His predictions for me to achieve the following grades were as followed (my teacher usually always has a very firm prediction, and 9.5/10 is right with what he predicts).
Coursework (A453): A
Coursework (A452): A (I don't know if my teacher remarked this coursework, would definitely go to an A* if he did, if not i'll appeal it on results day if I don't get an A overall in computing)
His predictions for me, keeping in mind I got 2 A's in the coursework
The below shows how many marks I'd need in A451 (the written exam) to achieve the respective grades.
C = 7-15 Marks, B = 15-20 Marks, A = 30-40 Marks, A* = 40-50 Marks
I'm sure if you insert your own coursework grades instead of mine, you can get a good idea of how many marks you'd need to get the grade you want.
As for OCR Maths, my personal prediction (along with some discussion with my teachers and friends are as follows)
C = 64-67 Marks/200, B = 99-102 Marks/200, A = 134-137 Marks/200, A* = 165-167 Marks/200
I may be off with the maths marks but, a lot of my teachers agreed that the exam this year was much harder, and that it's extremely likely that the grade boundaries will be slightly lower than before.
I hope this helps.