Leyla Akhmadeeva and I (Boris Veytsman) made several experiments trying to determine whether typesetting niceties influence reading speed and comprehension. Some of them are described here:
Our experiments were inspired by the great paper by Chuck Bigelow and Gordon Legge Does print size matter for reading? A review of findings from vision science and typography.
Basically we found that despite typographic lore there is no much difference between serif and sans serif fonts at the same font size and similar shapes. This corresponds to Legge and Bigelow's finding that size does not matter (as long as it is within the "comfort zone").
We did perform some experiments with justified and ragged right texts (we did not try different justification algorithms). We did not gather enough data yet to be sure, but it looks like the difference, if exists, is very small.
My opinion is that typesetting is driven mostly by aesthetics rather than by actual differences in reading speed or comprehension. Human brain is very flexible and can read almost anything. Or, as Legge and Bigelow think, over the years of typographic history the really unreadable styles just died out, and everything that survived is basically equally readable.