I don't know about this for sure, but I think you may be better off doing a couples match. The way I understand the couples match is you will match at whatever program you both rank highest that also has you ranked to match. If your girlfriend is applying to less competetive programs, she will likely be ranked to match at several programs, so she should match at just about anywhere you match. You might lose one, or maybe even two spots on your rank list at worst, but you will still match in Ortho and be able to spend what little free time you have with someone you love (or at least dig enough to want to couples match).
Going about it by just interviewing in similar cities and ranking is pretty risky with ortho and say family/IM/peds. Your girlfriends are likey to land their 1st or 2nd choice. If you don't get yours, you most likely will be in diffeent cities. Maybe if the urban is NYC and you plan on ranking every program in the city as your top choices, then you may have a chance, but most urban centers don't have that many programs. It is very likely that you could match at your 5th choice, we will say D.C. for example, but she lands in her first (and your first) Chicago.
Good luck guys.