I was told by many people to do as many as you can open book and then towards the end of October start doing closed book.
When you do them open book, you're able to actually learn what is being asked of you, so when you see a similar question in the VCAA 2013 exam you would know how to answer it properly because you've already gone through it.. Doing closed book timed exams doesn't allow you to do this as you really feel pressured for time. Also, I heard that simulating closed book exam conditions at home is beneficial, but it really doesn't exactly simulate real exam conditions. When you're sitting that English exam on October 30th, you'll be full of adrenaline and the whole setting will be different. It is vital to at least do some closed book though so you get an idea on whether you can roughly finish on time.
It is really up to you though and I'm no specialist, but that's how I'm going to be doing practice exams.