Question special

What are the career implications of purely clinical residencies as opposed to research track programs and physician-scientist training programs (PSTPs) for MD-PhD and MD-only students who want a career in science and/or academia? For MD-only students, are there opportunities to obtain PhDs during residency, or is that a less common practice now? For students who are only accepted into purely clinical residency programs, is it more valuable to do research for a year and reapply or else to begin clinical training right away (and perhaps plan on a research fellowship afterwards)?