Taking a different tack, to at least give the impression of greater sharpness, you probably would want to use a glossy paper. Apparently, any sort of texture will look a bit softer (but for portraits that would be good). The downside is that glossies have an "issue" with glare or reflections when viewed. To give the standard non-answer, our eyes can only resolve so far and anything more is gilding the lily. To further confuse things, higher contrast and colder tone can sometimes make a print look sharper, at least to some people.