Well, the distinction to me is that a lot of 3.5 play is looking things up, checking rules, and waiting to find out what happens next. Except for the spellcasters, most actions devolve, in description, to "I whack (shoot) the bad guy."
The difference is that in Iron Heroes, what takes time is figuring out what happens. Essentially, you burn game time as you burn "screen time." A simple action is simple. A complex action, such as taking a stunt, setting up a challenge, or using tokens, takes time to use.
The best example I can give is that Iron Heroes reads a bit like a matrix movie, or any other good action movie, where in the really intense action sequences, the film slows down so you can watch it, or you get to see it from several angles in succession. So that the FUN factor for the time spent is MUCH higher.
But that's my take.