This is something I've looked into exhaustively since ACGME pathology is often less competitive for DOs than FM. DOs MUST take Level 3. Because the merger is several years away and it will take several years after that for PDs and fellowships to "get comfortable" with the score conversions and knowing how to interpret them in terms of comparing DOs to MDs in terms of results, expect to take Step 3 also. Having step 3 done is just a useful check in the box for applying anyways.