What is the difference in these shafts. I see there is a small (almost insignificant) weight difference, but other than that its hard to tell anything from the true temper web site.

Other than the weight, they get a bit stiffer going from the 100 to the 400. I haven't hit all four back to back, but better players can tell the differece between an S400 and an S200.

I don't know if the bend profile is that different, but imho, the 400 keeps the ball lower than the 200. Part of that could be the weight though, as you generate a bit less club speed with the heavier shaft.