You're talking about the mechanics of filing the K-3 NOW, vs. waiting until you are together, getting married, and THEN filing the K-3. The calendar provides the 6 months difference. If you file K-3, you can also file K-1 after you get the NOA1 receipt (Notice of Action) for the K-3. Looking at it this way, there's about a 1 week difference (depending on the service center response time). There is, however, an additional stumbling block on the K-3 route in that it is an immigrant visa and is more likely to be sujected to an "administrative review", which could add months to the process. With the K-1, your SO is not a legal permanent resident until after you file AOS (Alteration of Status) and get the green card (2 years later). So, yes - go the K-1 route