Pace - I think ferrying is less stressful, one long flight where you fly the thing, rather than 4-9 flights with someone doing their best effort to kill you every time you come anywhere near the ground.
I think my most stressful was 14 x 30 min flights in one day.
2-3 weeks is very achieveable, in my experience it's the ground study that lets the student down, so it only works if they pass all the exams before they start the practical training. My shortest UK PPL is around 4 months.