I'm planning to do MD depth in October. Currently working through the 6MS for that topic and wondering if the best approach for getting up to speed on the T/F and HVAC would be to get the 6MS books for those topics and work the breadth problems or to work through the PPI practice problems for those topics. I want to spend enough time on the T/F and HVAC topics that I can nail the morning portion but I don't want to waste time doing PPI problems if they are going to be way harder than the problems I'll see on the test which is my impression reading through past posts. Any opinions?