There is no reason to use the +P 147 unless you can get it cheaper, then go for it.
Facts matter...Feelings Can Lie
Not better, but the +P does not give you anything extra.
Facts matter...Feelings Can Lie
For what it's worth, the extra momentum helps with punching through barriers. I've found that 9mm loaded to +P levels(124gr and 147gr) will punch through materials that standard pressure 9mm loads will not penetrate. For instance, a 124gr+P GD, the Winchester 127gr+P+ RT, and the Federal 147gr+P HST will punch all the way through a 6x6 piece of pressure treated pine(I am sure other loads at +P levels will have similar penetration performance). Usually the standard pressure loads in 124gr and 147gr stay in the 6x6 somewhere. That's 10 shots per load and they all performed the same. I have yet to find a .40S&W or a .45acp(or +P) that will do this. In fact, most .40 and .45 loads will not penetrate through a piece of 4x4 pressure treated pine. For FBI testing, I agree with Doc that in terms of those test criteria the +P probably isn't a game changer.
Velocity, elongated ogive, and smaller cross sectional area help it to do that. We had the option of going to .40S&W MP5s in the late 1990s, but part of our decision to stick with 9mm was that it was more accurate at longer ranges and it would punch through a wider variety of barriers than .40.
Unfortunately we see that often here, when guys are shooting from the 40 or 50 and don't get the round past the 25 yard barricade post.
I have also seen better penetration in other non-standard barriers. One reason why I like the 9mm for my needs as much as I do.