Yeah neurosurgery is still competitive even in the AOA world. I think <50% who apply for it get it. A lot of those applicants will have backup specialties. I'd say you def. need >600 on COMLEX. Of course there are the exceptions but usually those students are well connected or they spent a year doing a transitional year/internship first. Some programs may deny it, but depending on who the PD is they may look at your USMLE score to see how competitive you are. The AOA applicants who are personally know that matched were within the top 10% of their class, >600 COMLEX, honors on rotations, and had some form of research experience. There are a few programs that don't care about research however. If you want match ACGME the standards are even higher...and the match will be a crapshoot, your USMLE needs to be >245 to even have a chance. Letters of Rec are also very important as well so make sure you secure those early on in your 4th year.
Another factor to consider is the possible ACGME/AOA merge. From what I hear some programs won't make it past ACGME's accreditation standards so be weary of that.
I would be wary of speculating far ahead about what the ACGME/AOA merger will do. With so few spots and usually 30-50 applicants per year, I would advise you do as much as you can as early as you can. Many osteopathic schools are not located close to the programs so during your first two years crush all your classes and score well on your COMLEX. You can try and read intense neurosurgery texts but you will not remember them, so you need to focus on neurologic exam (knowing how to localize), dermatomes, etc.
Your third and fourth year should have at least 3 audition rotations and early. Each rotation should be at an AOA program and you should get a SOLID letter from each program director. If you'd like to know exactly what I did, you can contact me through my blog "TheParamount". Pick where you go well, it is well known which programs are flourishing and which are not.
I think research sets you apart, but it is not make or break like ACGME (don't even think of ACGME without a solid research CV).
While it is true that many candidates are >600, top of their class... this is not guarantee for neurosurgery. I have seen many candidates that are 550, top 25% etc, that WOW in interviews and do very well in residency.
Honestly, just as in med school, grades, scores, etc get your foot into the interview. The interview (and any audition rotation) with the program is what gets you into the program.
You can ask me specifically if you have exact questions.