Working too far is not worth it. First 4 chapters sounds reasonable as long as you take time to learn it well.
More importantly, brush up skills built in 1/2. 3/4 is very similar to 1/2, just a lot more application based.
Spend these holidays making sure there are no flaws in 1/2, and work on your overall algebraic and arithmetic competence.
I agree totally with shadows. I personally wouldn't go beyond 4 or so chapters. Spend the holidays finishing the allocated homework and consolidating what you have learnt in 1/2 Methods (which is about 50% of the course for 3/4). Areas of concern for Methods could be: trig, composite functions, modulus functions, sketching power functions, computation, algebra skills and transformations. I wouldn't be bothered to do anything on calculus or probability, as you will cover it later in the year - and, chances are, you will have forgotten some of the stuff by then.
Of course, if you really want to be prepared, try working on exam techniques and so forth. For example, find a good study area at the start of next year to make sure that you can concentrate. As you will no doubt hear next year, Methods is a test of how well you can do tests, rather than a test of your mathematical ability. Many of the questions aren't that difficult, the concepts aren't too hard either. What differentiates the good from the best is one's ability to read questions carefully, to avoid making careless errors.
Hope this helps!
