What these people are trying to tell you, politely, is that there is no reason to use +P+ ammo.
+P+ ammo has no SAAMI, or CIP standard. Winchester and Federal try, key word is try, to keep the PSIA to 42,000 psi.
What additional effectiveness are you thinking you will see by going to +P+ loads?
The point is not that the SD line cannot handle +P+, because it can, the point is just how long do you expect your pistol to last when firing near proof loads? You will be taking thousands of rounds off of its effective life for no real increase in effectiveness.
You do not shoot for COM, as there is nothing in the COM that would stop a fight. Aim for the Thoracic Triangle Area between the armpits & throat.
Platt was shot by SA Dove and his 115gr Silvertip caused a non survivable wound (at least non survivable w/o immediate medical assistance). Platt was able to use his Mini-14, despite being shot multiple times, and kill numerous FBI Agents.
The reason why 12" is the FBI minimum is because of cross torso shots, or shooting through intermediate objects (light concealment or arms). The 4 layer denim test is considered a "worse case" test for evaluating bullet performance. For an armed civilian, the chances of you needing to shoot at an automobile is a lot less than an LE officer, not eliminated, just lessened. If a load was reliable and accurate out of my pistol but penetrated on the light side when tested in 10% gel (say 11" to 13", as opposed to being 13" to 16" for most LE loads), I would not lose sleep over it.
Were I you, I would get some professional instruction and learn to shoot well. Then shoot a number of SD/HD loads out of my pistol to find out what is the most reliable and accurate, then buy a couple of cases of that load.
To a great extent it is the singer and not the song.
BTT, I have carried +P+ (specifically the 127gr Ranger T load) in many 9x19's and I still have 10-12 boxes of it in my basement. I now use either std., or +P, loads, depending upon what 9mm we are talking about, as I got nothing but increased recoil and muzzle blast from shooting the +P+.
As always you are free to differ and go your own way.