My argument against using UW on the shelf exams is exactly that...to save it for step 2. If your whole rotation grade depended solely on a shelf exam, then I'd say use what guns you have for it but it doesn't. More often than not, the shelf exam encompasses less than 50% of your grade (this may be institution dependent). Aside from UW there are a lot of other great resources for shelf exams like pretest for some, blueprint cases for others, or case files or MKSAP for IM. Therefore, UW becomes merely a secondary if not tertiary source. Something you do when you have spare time or run out of other things to do.
However, UW for step 2 is the KEY question bank. Exposure to more questions usually = greater results. You can memorize the question but that doesn't mean you can manipulate that information and answer another question correctly. People who do UW twice for step 1 and get significantly higher % average 2nd time around, usually perform to whatever correlation their first run percentage is any how with maybe a few point increases.
I believe doing 2 different Qbanks would benefit you the most because you get exposure to more types of questions as well as saving UW for the end. Performing well on rotations require more than just UW but performing well on Step 2 depends heavily on good use of UW.
questions that I wound up doing 3-4 times b/c I kept doing them until I understood them during 3rd year.
