I work as a Research Analyst in the Financial Services vertical at McKinsey. From my experience, I can tell you that the role and the career progression are quite different from that of an associate level entry.
Research Analysts are not hired into the partner track (however they have started to change this); they are trained as knowledge experts in a particular domain from the day they are hired. On the other hand, associates start as generalists and develop expertise in a particular industry as they rise to EM levels.
Moreover, a transition from a BO role to a consulting role rarely happens and depends upon vacancies, ability to deliver stellar performance and rapport with the partners. In short, a very rare event. Most of the people that are hired into the research analysts move for higher education (MBA) and then try to make the transition.
I hope this answered your question. Thanks!