Just throwing this out there, but I would NOT recommend doing poorly in classes.
I didn't study obsessively, and I mainly focused on topics that I suspected might be on the USMLE. Eventually, I feel like I gained somewhat of a 6th sense for "boards-worthy" material, and focused on that. Still though, I put considerable effort into my classes. I wound up probably 80th or 85th percentile in my preclinicals (which are pass fail by the way). The fact is, the score I achieved on boards would NOT have been possible if I had slacked off in classes. Classes are where you build a strong base, and that's where a large portion of the heavy lifting gets done, in my opinion. Then, for boards studying you refine your knowledge and your test taking strategies. But I would never slack in class to prepare for boards.
I guess, more specifically, I would never slack on the CONCEPTS. It's ok to slack on some of the details. For example, we learned in depth about management of mild vs. moderate asthma, or guidelines for mammography and when to biopsy breast lesions. This material will NOT be on step 1, and I knew that, so I skipped it. But when we were discussing the HPA axis, or the findings in pituitary vs. adrenal hypocortisolism, I spent a lot of effort trying to achieve deep understanding with that. And that all happened during my classes.
Fact is, FA is just a list of facts. Reading FA and thinking you'll ace boards is like reading the dictionary and thinking you'll have a good vocabulary. The best way to get a good vocabulary is not to try to memorize the dictionary, but to READ A LOT OF BOOKS so you gain a FUNCTIONAL knowledge of how the words work with each other. The brain is much better at learning that way than it is at learning lists. And that functional knowledge is best gained during class.
Sure, you could not study your lecture material at all, and only read FA during preclinical. I heard of a guy who did that. But I don't think that would be effective; that's like reading the dictionary. Instead, focus on class, especially the CONCEPTS, and gain functional knowledge. Then, just refine that during your dedicated study time. Any boards studying done during your preclinical time should just be on top of what you've already mastered from class, not instead of it. Just my 2¢