Maybe it's put too simple, but perhaps you can say that while the bend curve of a mast tells something about HOW it behaves loaded (for instance a gust), the stiffness of a mast tells something about WHEN (under which load) it starts behaving according to its bend curve.
Given that the sail/mast combination is properly designed this means that a softer mast "breathe" or dump the power sooner in a gust than a stiffer mast. A heavier and stronger sailor with a relatively soft mast shall probably feel that he could handle more power in a gust, while a lighter sailor with a relatively stiff mast shall probably feel overpowered. Please correct me if I'm wrong.
As to the Warp 8.0 2010 and masts: I sail a Warp 8.0 2009, and I (well 80 kg) much prefer it rigged with a Platinum 460 + "Xtender compared to a Platinum 490 mast.
As to the Warp 9.0 2010: The specifications written on the sail say 524 +/-1 cm in luff length, but the sail my son have doesn't have a luff length much over 520 cm.