Step II or Sub-I for first block? Struggling...

Yeah, that's interesting. The consensus amongst the residents here is that ~1/2 programs nationwide start to download/evaluate applications on Sep 1st, whereas the other 1/2 wait until the dean's letter. Assuming that my CK score doesn't show up until mid-Sep, can I rely on the notion that the early cohort of programs will find out and/or care about my score? I would notify them, of course...

Whether or not you decide to take Step 2 early or not, one thing to consider is that you dont necessarily need the score to be released by Sept 1 to be early. The majority of programs I interviewed at didn't send out invitations to interview until after Nov 1 when the deans letter comes out. With that said, depending on your school's schedule you could probably do your home sub-i and maybe even an away rotation or so before you take Step 2 and your score would be available to the majority of places you apply to before they make decisions for interviews.