There are far more variables here to measure. First of all what constitutes that fifty you are thinking of rolling out? Lets say you arrive at it and what's next? For an engaged user the AB testing can measure up as you can define clear set of tasks and desired outcomes. But as i stated above, good type often goes invisible. People engage with the content and the not the,medium to tell you anything tangible. One cannot take away the subjectivity from the process when there is not anything tangible to measure.