A 3rd party book [*Advanced d20 Magic*][1] introduces a DC-based spellcasting system called Dynamic Spellcasting. What it basically does is letting spellcasters use their magic at-will, which is set back by a Spell Drain feature - each cast deals some non-lethal damage to a caster (the amount based on a pretty high Fort check), which by default heals only the same way as Ability Drain (natural healing only). The way it looks, it's a really interesting magic system that can scratch that itch caused by the sub par Truenamer mechanics.
  
What I want to ask is - how does this system compares to the classical Vancian Spellcasting? If we take two level 10 sorcerers with the same spell selection and put them against each other on an arena or give them the same task, will one of them feel overpowered next to another?  
  
The way I've figured, the HP problems of the Dynamic Sorcerer may put him on the same-ish field ad the Vancian one even through he can cast his best spells more often, but I'm not entirely sure of this.

  [1]: https://en.wikipedia.org/wiki/Advanced_d20_Magic