You got it wrong... 50Hz is Vertical... but as some owners here say the picasso can up that to 60Hz so it's in the 56-75Hz window of your monitor (Don't own one so can't confirm this though).
The Scandoubling thing is the horizontal and on stadnard Amiga this is 15.75Khz but with scandoubler it gets up to 31.5Khz so it too get in the 30-81Khz window of your monitor.