I have to confess to being a selective reviser - I've done it since I was a first year undergraduate and its served me well. I did Public, Crime, Contract and EU last year (I'm on the part time GDL) and I revised 3 topics to answer 3 questions in all topics except Crime where I studied a couple more because I was prepared for some questions to include a mixed bag of offences.
The questions on all papers were exactly what I expected - they were all problem questions and the crux of the answer was the same as many of the past papers even though some of the scenarios were quite different. In my contract exam, even though the questions were what I expected my mind went pretty blank on the case law front by the time I answered question 3, and I know I scored poorly on that - fortunately my first two answers which I had practised to death were pretty kick ass to it all evened out.
So based on that I would look at past papers, write out practice answers until you can write them in your sleep (and make sure you can answer them within the exam time period), if you start doubting yourself, study an extra topic as a fallback though maybe not in so much detail as the others.