Extremis Iron Man was probably the pinnacle of Tony Stark aside from Ax Iis Iron Man.
That upgrade was never really sustainable outside of the original story. This was before Marvel went down the gutter, and Iron Man didn't jump down a tier with every new armor. He was still a heavy hitter, but with an even bigger software upgrade.
Who'd win in a comic, Iron Man or the Flash? That's a tricky one.
Ellis has done a helluva good job with that story.
Then Shane Black ruined it in IM3... 🙁