From what I can recall, there's been published research on this and it says quite clearly that on average the people who do best on STEP 2 take it within a few months of STEP 1. There's so much carry over from all the bugs and pharmacology that people cram in via rote memorization leading up to the exam that people forget a ton of it when they take it 6+ months later. That goes for all the things you are learning on rotation as well.. so in that regard pushing it off 4 years would certainly be ill-advised for the average student. I'll look for the papers, but there's definitely been a few of them. I actually found out about this very thing from people posting links to the research here and on the subreddit.
edit:
Introduction: Graduate medical education program directors report that United States Medical Licensing Examination (USMLE) Step 2 CK exam scores will likely have greater importance in the future selection of residents due to USMLE Step 1 transitioning to a pass/fail score as early as January...
www.cureus.com
A paper that indirectly correlates STEP 2 with STEP 1 tests, and sites 4 papers that more directly correlate it. These are those 4 papers:
We undertook this study to determine whether a decrease in the amount of time a third-year medical student spent in an obstetrics and gynecology clerk…
www.sciencedirect.com
No abstract available. Created Date: 19 November 1997; Completed Date: 19 November 1997; Revised Date: 18 December 2000 © 1997 by the Association of American Medical Colleges
journals.lww.com
sion model to predict performance on Step 2 using gender, Step 1, and grades in medicine, pediatrics and obstetrics–gynecology was developed based on the class of 1999. Analysis of covariance was used to test the effect of time on scores, adjusting for predicted performance. Results. Step 2...
journals.lww.com
The consensus is "sooner is better than later" when it comes to STEP 2CK, and that's within the confines of a typical MD curriculum where sooner means within months, not the 4 years which you are talking about. You could argue that.. well, you could argue plenty of things, but if I had to guess it would probably be better to not be finishing up your PhD while trying to remember some bugs and medications you learned half a decade previously.
