get minimum, recommended pointsizes of a font

wakiki

I try to scale a qfont f.e. "Arial", "Bold" down, but i get ugly results with PointSizeF lower than 5.
The spaces between letters starting to get irregular.

I couldnt find something like minimumSize() so i tried this:

QFontDatabase db;
QList<int> standardSizes = db.standardSizes();
QList<int> smoothSizes = db.smoothSizes(_font.family(), _font.styleName());
QList<int> pointSizes = db.pointSizes(_font.family(), _font.styleName());

all lists have the same content from 5 to 72, so i guess the best way is to stick to these sizes, right?