More knowledgeable people will chime in after me, but, as I understand it, certain competitors prefer to use flat nose projectiles for shooting steel plates because they apparently transfer the energy better to a steel plate (FN bullets knock down steel plates more effectively).
It seems that hollow points are preferred for self defense because they limit overpenetration while simultaneously increasing the diameter of the wound cavity, thereby limiting collateral liability and performing better on an unarmored assailant.
Considering that:
1) energy and penetration combine to determine the degree of terminal effects,
2) cavitation has a greater terminal effect than the actual wound channel,
3) and considering that you're forced to use a non Hollow Point projectile,
I would say that, unless you're preparing for armored targets, over penetration is your largest concern. I expect the data to support the use of heavier projectiles. If FP projectiles transfer energy faster, it stands to reason that they are less prone to over penetration.
So I'd think that a FP is better, but I'd want to use 147gr and up projectiles (if limited to 9mm) as long as I know my gun will run them.
Unless you are preparing to engage targets at extended ranges, I would expect that the twist rate of your barrel is irrelevant for this purpose.
