Looking at a 38Fountain L, 525s stag, ITS drives, with stubbies turning 5 blades. What are the advantages of this config over standard Merc Racing XR drives. Obviously the stubs get me to max velocity but what about hole shot, mid range x/cell, handling and low speed manuvering ?

All of these questions are dead on. The decrease in drag from the cases being low will hopefully aid in top end. Using the 7.5" additional set back from the ITS should help the the props to hook up a little better because the water rises.

However, testing the boat and obtaining the actual performance data is the only way to know. Sometimes higher isn't always better.