The Pennine way in a week is averaging over 35miles every day, that kind of fitness and stamina only comes with endurance training and knowledge of the Peninnes.
With my past experience of long distance walking, averaging close on 40miles every day in goodness knows what weather, is beyond most of us.
Nine people have now completed the Pennine way in under 3 days which involves virtually continuous running with possibly less than three hours sleep in that 72hrs, from start to finish, and three have completed a back to back Pennine way in your allotted 7 days.
Dare I say it, but to complete the 270+miles of the Pennine way in a week, you will need to travel very lite and run certain parts of the easier sections.
To complete such a task would involve several attempts on completing the course, as well as having some support with friends providing food and beverage.
It could be done, but only if your incredibly fit, and know the path incredibly well.
Mike Cudahy the first man to break 3 days only managed it after seven attempts, there are certain sections that are very difficult to navigate in bad weather, and loosing your way when you know you have to average 38miles every day, will put pay to your 7day time limit.