To add to those good points that have already been made...some things you should consider.
I am contemplating taking an MSTP acceptance my school's program just extended to me (I am an MS2). I want to go into academic medicine for absolute sure and I am almost positive I want to go into surgery, specifically neurosurgery.
I admire your zeal, but you may change your mind in MS3. Nearly everybody does, no matter how gung ho they were about a particular field.
Is it feasible to skip the MSTP and do a PhD during a surgical residency, or at least enough research to get a K01 funded? I love research but I am tearing myself up trying to decide if I should take this and what is best for my future career.
There are a few surgery programs that do this. As I understand it, they are typically in Gen Surg and not Neurosurg. Like debateg says, if the Neurosurg program does not have an established track record of doing this successfully, caveat emptor! As Watson mentioned, oftentimes the "research years" of surgery residency is a euphemism for a decreased clinical caseload along with the time to write some case reports and do a few case-control studies.
You'll notice that most community and lower academic Gen Surg programs are 5 years. Then at a few of the "top" schools the residencies are 7 years, no exceptions. Two are "research years". I have a hunch that these "research years" were added onto these programs as a way of mandating an additional two years of indentured servitude to these departments. They are now taken as indispensable at these programs. I'm skeptical. An alternative hypothesis is that the two "research years" were introduced into these programs because burn-out and all the associated issues was so high that they provide a more reasonable work-life balance to keep people from dropping out. Who knows.
Point is that it seems to me that these residents on their "research years" are very often doing relatively light research. Very, very few do hardcore basic science. Is this what you intend?
If it is not, Neuronix et al. have made a strong case here that there is no reason to get a PhD for clinical-oriented research*. And if it is, then you should think long and hard about whether a career doing both surgery and basic science is feasible. Certainly there are people who do it - and do it very well - but the vast majority do not. In a field with exceedingly long hours, exceedingly lengthy training, and exceedingly high reimbursements, the pull to do clinical medicine can be overwhelming.
Good luck.
*No pragmatic reason. Pure intellectual curiosity is not pragmatic but is a good reason, as long as you realize that from a career standpoint the PhD will likely be largely irrelevant to clinical-oriented research.