If your goal is to do well on your subI, I personally doubt that either SICU or rads will be particularly helpful. I would just do something relaxing (like psych or rads) so you start out your sub-i energetic and enthusiastic and, if you want, use the extra time you've got on your hands to prep for whatever pimp questions you might be asked on your sub-i. Although if you really feel you need extra clinical preparation, I think a true surgical elective (maybe vascular?) would be much more helpful than SICU or rads.