In "Obsession," Spock tells Dr. McCoy that "fortunately, I read somewhat faster (than you)." Is there any evidence, in-universe, of how fast Spock can read? McCoy doesn't doubt Spock, and being a Vulcan, it seems safe to assume that he can read faster than most other known humanoids. Obviously he can't read anywhere near as fast as Data, though.
In TOS episode 'Where No Man Has Gone Before', the mutating Gary Mitchell has a reading speed beyond any humans (and implicitly Spock's) which is shown as amounting to eidetic memory at a glance.
Spock's own words which we must take as logically accurate are that he reads 'somewhat faster' than McCoy. This does not imply any vast superiority.
Somewhat is defined as:
"adverb to a moderate extent or by a moderate amount; rather. "matters have improved somewhat since then" synonyms: a little, a bit, a little bit, to a limited extent/degree, to a certain degree, to some extent, to some degree, (up) to a point, in some measure, rather, quite, within limits;"
Spock's speed is probably therefore at human limits, not superhuman. Perhaps about that of John Stuart Mill - who lamented that he could not turn the pages of a book fast enough. Spock and any Vulcan would probably have better retention and comprehension at the same speed as a fast-reading human. 1,000 to 2,000 words per minute, equates to 50% comprehension in fast reading humans. https://en.wikipedia.org/wiki/Speed_reading