The thing with cloak is that if you don't change positions after using it, enemies will still hit you because they just shoot at the last place they saw you. Cloak, change position (just a little will do) fire off a power (incinerate, sabotage or your any stunning or damaging bonus power) then quickly get off a headshot. I can kill an banshee in three or four shots like that. Less if I co-ordinated the squadmates' powers to strip the barriers first.
Also, something a lot of people don't seem to realise is that for an infiltrator, weapon weight and cooldowns don't matter. So long as you interrupt your cloak before it runs out on it's own, your cooldown will always be the same. This means you can equip as many weapons as you like, including ARs & SGs and you don't need to bother with the 'ultralight materials' mods. Just make sure you ALWAYS cloak before you use any power. Since doing so give you a damage bonus anyway, there's really no reason you shouldn't.
It also matters which squadmates you choose, how you equip them and what you're up against. The mirror matches are all about stripping defences, so you want them to have a good range of powers. Overload and shield drain are obviously best for stripping shields, warp is great for both armour and barriers, plus it can both detonate and prime for explosions. Reave works well too since it's also an AoE, so combined with singularity it's can be devastating to small groups.