It depends on your situation. I have taken PTs from PT 20-70 so far but only because I had started prepping a year in advance. Of course, even if you have 1-3 months before your exam, you can always do more PTs/week to be able to do PT 50 onwards. It's all up to you, do you feel like you need to do 50 PTs? Or just 10-20 PTs?

At least for me, I've been taking 1 PT a week and reviewing it to fully understand my errors and weaknesses but I do plan to take 2 PTs a week for my last month of prepping, so I can get use to the atmosphere of exams. Nonetheless, by the time I'm done, I'll have done PTs 20-90.

I would be interested as well. I am also taking the June Exam.