Any advancements to a 9mm HP would also apply to a 40
9mm typically recoils less and holds a round or two more
40 hits harder and makes a bigger entry hole
I feel more comfortable with a 40 than a 9mm
Strive to always carry the gun you would carry on the "bad" side of town.
My carry philosophy is "Something is worth doing is worth doing right" not "Something is better than nothing".