Hear is what I know. At the UCSF IM interview session where they talked to us about applications and what not, NO ONE stressed to us to make sure Step 2CS was completed prior to ranking. We received an email from admin that stated that we had to take Step 2CS prior to our last block (basically by April) and Step 2CK by March 1st. As far as I know, it is a rumor. Go to program websites, if it was a requirement it would be in boldface all over the place.