Decided to throw a GPS on my Salarian Infiltrator instead of the Widow for a few rounds, and my god Infiltrators are ridiculous with that gun. Between not having to reload after every shot, being able to charge up a shot before cloaking (the timing I still need to get used to though, I've been immediately uncloaked quite often), being able to do more damage against shielded opponents on Gold due the mechanics of shielg gating and shotguns, and the shorter ability cooldowns, I am just loving it. On the other hand, I need to hit the ammo crates more often, and the Widow is much better at longer ranges, when you can't actually target the opponent (and the GPS has a much bigger spread), or when the travel time of the GPS starts causing missed shots. But it's a very fun and viable playstyle, especially if you're not so great with headshots.