I'm an undergraduate currently. I am looking to pursue a PhD next year. I have an established PI here who I have been working very well with, and we already have, well, probably at least 2 years in the future worth of plans for potential projects. Obviously, it often does not look good to do your PhD at the same program as your undergraduate, as I have read that institutions view it as though the student does not want to leave their comfort zone, will have a more restricted network, fewer diversity in the background of recommenders, etc.
The problem is, my undergraduate institution is number one in the field I am doing, and in the graduate field I hope to pursue (its "specialty" is a different subfield than mine, but I am sure it is still at or near the top of the specific subfield I work in, and the entire program itself is still number 1). So my question is, could it potentially harm me in pursuing my PhD at the same place? What potential impacts could it have on me down the line? If I have other connections that I also have worked well with in the past at, say, the number 10 school in the field and am accepted there, would that be better, worse, and why? If I could instead work in a similar field at a different campus of the same university that is also top 5 (and also would allow me to perform the same research, take as interesting and focused coursework, etc), and my current PI would be able to co-advise me with a faculty member from that department, would that change things and be "far enough" of reaching from the undergraduate institution?
I am not at all concerned with rankings, but obviously with the current pay structure and employment market in academia, that is not something that can be taken out of the equation. I agree that I really enjoy pushing my comfort zone as well; at my current university, The only places with that sort of funding for the area of research I perform are top 25 schools, and getting hired by one of those is obviously a majorly uphill battle to start with. I really appreciate any insightful feedback/suggestions/tips you guys can give!