Read what Mauricio says about superflex pens........he sells them, and says 9/10's of a pen with great flex is the perfect set up of nib... in a fast feed and proper distance in the pen section. A lot of little fiddling work....so don't go yanking the his set up nib out...because your DIY will not be up to Mauricio's snuff.
In Superflex my problem is it is very hard for me to write EEF (I need a helium filled Blimp attached to my hand to write that light).....EF requires thought and care...and I'm still a bit heavy handed, so often I end up with my Waterman 52 writing to a F. I could take it to BBB....but only take it to BB...........in I have read Richard Binder's great article of how to spring your nib and cost your self $$$$.
I have a 100n that will go out to 5X....after testing that...and I do have a small bit of experience in feeling how much is enough, I never go more than 4 X.....in having read Richard's article I don't want to ruin a nib by stressing it to max often enough for metal fatigue to ruin a nice nib.
As mentioned often enough...folks no one has ever heard of are showing how much they can max a 'flex' nib. ,,,good possible showing you how they over flexed the nib.
Those who can write is Copperplate or Spenserian....not me by a million miles, are more interested in quick snap back narrow line than how wide they can make the nib go. There is a subsection for them.
There was a great thread somewhere on the com, where someone found that Waterman in the '30's was after a lot of tine bend to go with 3X tine spread......................so it could well be true we are all over stressing our Superflex nibs.