Jakester
I may not have an exact answer for you, but just another consideration. I'm an '09 USMA grad and am still serving as an officer, so my cadet days are pretty far behind me. But I will tell you that if you are serious about the academy, you need to do swimming your senior year. Here's two reasons:
1) A HUGE discriminator during selection is your participation in sports and whether you had a leadership role on any teams. Something like 90% of cadets were a team captain at some point. It will definitely benefit you to do swimming again senior year and be a team captain.
2)Your grades are important, absolutely, but when you get to the academy, you're not going to get the option to take it easy physically just to focus on your grades. You will be expected to do your academics, play a sport (even if you're not on a varsity team you have to play intramurals), and maintain your military lifestyle. I worry that if you take it easy physically now, you wont be ready come go time at Beast. During your first summer, your physical condition will matter much more than your academics.
I'm excited for your adventure, my time at USMA was amazing (very tough though). If you make it check out the skydiving team, it's the best gig USMA has to offer!
If you have any other questions please let me know. Also, there is a cadet training website that has a great article on it about studying and time management, its cadettraining.net. It may help you with keeping things going senior year!