I was going to take SICU during fourth year but then decided to take anesthesia instead. Can't say that a SICU rotation won't be useful, but i don't think it is necessary as you will learn to deal with SICU patients as an intern during your rotation ( at least I did). It can be a little overwhelming at the beginning, but after the first week, you'll get the hang of it. I suggest you enjoy 4th year a little bit and take lighter rotations especially towards the end of the year.