The 1K fps muzzle velocity has usually been the bench mark for reliable expansion. Under 1K and bullet expansion is more unreliable. The XTP HP's have a rather shallow cavity and that inhibits the expansion somewhat. Testing a few in gel, water or wet pack from the .38 spl for expansion is the only real way to tell.
You would be more likely to get better expansion using a conventional design JHP from Remington, Nosler or Sierra at 1,000 fps than a Hornady. Other good bullets for the .38 spl are Remington Golden Sabers and Speer Gold Dots.
I load my 125gr .38 spl +P's using 6.0grs of Unique that produces velocities around 1,050 to 1,080 fps from a 4" revolver depending upon bullet and gun.