What would you define as faster? That's relative as what you would consider slow growth others might consider it explosive growth :-)
Also, all corals grow at different rates and they all require slightly different conditions. As reefers what we constantly try to do is average everything out so that mostly everything in our tanks are happy. However, this doesn't mean that the conditions are exactly ideal for any one coral. The bottom line is so long as your tank is stable and you're doing your chores you just have to sit back and wait. And wait. And wait somemore :-). One day you'll F'ing yourself at a point where you wished your GSP and Xenia grew slower! Or better yet, stopped growing altogether
...seriously, damn GSP..