A lot of people consider the damage and debuff of powers without considering the stagger associated with it. PM is a fairly decent staggering power which gives it added utility when you know how to use that. There is zero way in hell you should ever consider skipping it on an infiltrator, IMO.
As far as GI play, I prefer pistols on her personally. She is a great SR platform but I eradicate things much faster with a pistol mainly the Talon on her. Good base shields which makes cyclonics even more effective on her if survival is an issue. Always max HM because of the movement speed, damage/accuracy, and awareness of it makes it one of the better powers in the game.
Generally surviving is accessing the situation quickly, disposing of the enemies fast, then moving on to the RHA spot. It's basically getting to the spawns in a good RHA spot kill from front to back, right to left. What does that mean? GI can OSK most anything so I will triage a little differently bc I can kill so fast, I might prioritize phantoms and goons as more important with another kit but with a GI I kill whatever is closest to pushing me out of my RHA spot first then from R to L because of lanes of fire changing to push you off the RHA. Phantoms and goons are still one to two shots in most cases to put down. Atlases or other bosses in sets of two, screw them I rocket them; not necessary with the GI but if I'm playing her the enemy has called down the thunder anyways so death is going to happen in mass quantities.
As far as setup, straight up AP rounds for pistolas IMHO, damage barrel with clip extension on the Talon for me. I might even throw on a Harrier as well just to have something else to kill with when I get 75 pistol kills.
Another thing is realizing that when your shields break if you have aggro on you, you're dead.