Youre a senior. Get Drunk, go party, do your elective in "how to sleep in and not go to classes on friday."
People in their 4th year of medical school make the same mistake you are making. They beleive that doing a Sub-I month in an ICU will somehow give them an advantage when they arrive in their residency and are asked to do a month on an ICU rotation. THe amount you learn as an Intern in the ICU is 30-40 times what you can learn as a medical student in that month.
You are taking an undergrad course with the intention of getting some advantage in the medical school. Don't bother. You can read an entire immunology textbook in undergrad, only to realize the emphasis is different. You'll likely be taking a PhD-type course, which is TOTALLY different from medical school. The small advantage you will have for one class is not worth your sacrifice in your senior year of college (the best year of your life).
You will be in class 4-8 hrs a day, reading another 4-8 hrs a day, relearning everything you thought you knew in a manner that your school wants you to learn it, only to relearn it a third time for the Step 1. Seriously. If you can get away with taking a bull**** gut class, do it. If you really have to, take the one thats easier and meets the least amount of time.