They are pretty close in how fast they are. However, the Sage is a far smoother and nicer rod to cast. The St. Croix is medium-fast (like the XP); but it feels like you have to push it to cast it well. The Sage just applies the casting energy in a very smooth manner and as such is far more enjoyable to cast any length of time.
The newest, top-of-the-line St.Croix is an entirely different matter. It is a fast-action rod that has the smooth power application experienced casters like. Unfortunately, the SCV does not have this characteristic.