I know where you are coming from as one instructor of mine always said that anything above was a waste of effort, But hey whats wrong with doing the very best you can and feeling proud of yourself? Whay aim for 75% just because that is the pass mark? At school I was always told that if I wanted to pass with a grade C then I should aim for a B and if wanting a B then go for the A.
I had heard in the past that BA were unlikely to look at you if you got less than an average of 85% - don;t know how true this is, just something I heard. So, could always ask them the same, well 75% is a pass, why you want 85%?
All I say is give it the best you can and good luck.
Regards.