Other than offering a modest gain in velocity (RA9T goes 990 fps, P9HST4 goes 1050 fps), I don't think that the +P 147s bring very much to the table. Sure, having the extra 50-60 fps can't hurt, but I've seen standard pressure 147s run that fast (depends on the gun since ammo is loaded to pressure, not velocity) and the effect is simply not that much greater. That extra 50-60 fps might get you another 1/2" to 1" of penetration- it's just not that much in the grand scheme of things.
Don't get me wrong- I like the 147s in the 9mm and carry 'em all the time. So long as you don't delude yourself into thinking that they (the +Ps) are capable of more than they are, I say have at it and carry 'em.
