Use the Kaplan books solely for content. Incorporate the Kaplan CARS strategy into your studies and determine whether you like the strategy or not. Not quite sure what the lesson plan books are but the study plans on SDN seem to be godly. Stick with Kaplan/Khan, content will be same for every company, just worded differently with different test-taking strategies. Focus on FL tests, that's where most of your money should go.
Best of luck.