I did none of the study before heading out to the US for my PPL, although I was halfway through an Engineering degree so the theory was not exactly difficult; I'd also been interested in flying for a while, and so I was familiar with the basics through Flight Sim. I studied for an hour or so a day as well as flying, and got it all done in 4-5 weeks.
The more I hear from different people about how they studied for this, the more I think that it's unique to the person. However, it's not going to hurt to do as much as you can in advance; you can never know too much! If you can do it all before you go, then you'll just be more relaxed while you're out there.