I would recommend you choose a more American-like model where the duration of the PhD can be longer. There are several reasons for this:

1. You want to be as strong as possible when you start seeking a job. Who do you want to compete against? Someone who took 2--3 years to build his research program or the guy who took 5--7 years? You can be sure that the later is much better prepared to apply for funding, supervise graduate students and so on.
2. You want to give yourself room to grow and have a margin of error. Some people do great research within 2 years... others take 5 years before the they fully bloom. You can really screw up in research sometimes (through no fault of your own). Having a margin of 2 years is very thin.