Don't bother unlocking the infiltrator with the recent patch.
The silenced pistol used to kill light suits in 3 shots, and heavies in probably 12 or so. Now it takes at least twice that, if not more. And the SMG is a bit more accurate, but the damage from it isn't that great either. It's better than the pistol, but still doesn't even compare to other classes weapons.
Saw an enemy sniper, and started popping him with the pistol. I got 3 shots into him before he started moving, then another when he flew off. Chased him to try to finish him off, but another sniper shot me while stealthed thanks to your skii lights showing even while stealthed. Might have done better with the SMG, will have to try that next time I see a stationary sniper.
I then went to the enemy base, blew the generator, and a heavy came to repair. I stabbed him in the back, doing about half his health in damage, then emptied two clips of my SMG into him while running and jetpacking circles around him. Almost killed him, but he finally caught on and fired a single spinfusor into the floor and killed me with the splash damage while I was putting a third clip into the SMG.
The melee backstab still works OK on lights and mediums if you can get up to people as long as they don't have the perk that reduces melee damage, but the main guns are pretty terrible. Dieing to one melee shot makes stabbing some people rather dangerous, earlier I backstabbed a sniper who survived due to the perk and immediately flipped around and one shotted me with melee before my character even put away his sword after the melee swing.