I was searching for something unrelated, and ran into a symposium from last year...
Looking back, I find it interesting that exactly one respondee said that they would take Zambrano in a big game (over other Cub starters). I really liked the ERA+ and Size similarity comparison that Tinkers2Evers did.
Over the past year, I've come to consider Zambrano to be somewhat similar to Seaver. Although Seaver had a different motion and pitched up in the zone, he was a large man who punched out a lot. He allowed a few more hits while allowing many fewer walks. Like Z, he was worked very hard in his early years, and it's arguable (see: The Diamond Appraised) that his post-30 effectiveness was greatly reduced by his early workload. That's a scary thought, when you consider how good Seaver was, even with this "degradation" in the middle of his career. We'll have to see what happens to Zambrano.
I think I'd take Zambrano #1 for a big game.
On a side note, Zambrano's 2005 season was interesting... he's always been LESS effective when he throws harder, since his ball sinks less. And his velocity was noticably higher last year on a consistent basis. I recall very few 92 MPH pitches last year. To me, that speed seems to have maximal sink, and is almost unfair to the hitters. And when he's going good, he seems to be able to throw it almost effortlessly. Before 2005, I would always hope he would make it through the first inning or two, when he would invariably overthrow, because once the velocity came down a little in the 3rd and later innings, he was nasty. In 2005, his velocity sat at 96+ for the whole game virtually every time out (and I watched most of his starts).