Charles Darwin was an INTP 5w6 so/sp, I think.
i don't know about so/sp, but i would think this is a very good guess.
i would put marx as intp 5w6 so/sp, but so/sp is clearer based on his social philosophy, his obsession with class, and his critiques of hegel. bc for marx (and what i imagine to be so/sp), in an absence of true sharing, the felt absence of privatized desire, authentic will, sx presence, creates a kind of disfigurement. for
my necessary sense of community to be controlled by the private desires of other individuals in ways that undermine the communitarian values that i hold is simply unacceptable. because i will always feel used, rather than a sense of authentic belonging, authentic brotherhood, etc. in the end, i fear that you will always try to take more than your share, claim possession, and grow your own private wealth at the cost of my own. darwin i don't really have that kind of evidence to make a judgment.
furthermore, 5w6 have an appreciable rigor and consistency of inquiry, whereas 5w4, while rigorous in their quest for truth, follow a process that is often far more about themselves. more of a quest for self-mastery as a form of self-expression. 5w6 are the ultimate science-for-the-sake-of-science scientists. i often rely on their work, because it is the most grounded.
and personally, i think 5w6 makes you intp, intj, or istp. the positing as deductive, but actually equally constituting functional explanation to me feels very similar to marx and very similar to the explanations given by the intps i know. they get off on really casting the lure quite far when they are testing a problem. what if this class of stories, and this class of stories, and this class of stories are not the answer? what are the differences between them? what other possibilities could exist? so really, i guess, it's the stories about stories process that seems to create layers of possibility and start to weave together seemingly functional, circular explanation in the form of deductive inference. a necessity to create grand meta-narratives like "evolution" or "historical materialism"