Infected is a different matter. Never succeeded there.
You have to kill all Borg very fast, and be at exactly the right spots at the right moment.
Basically, you have to split up your team. Two take care of the workers and save the redshirt, while the other three deal with the other drones, especially the heavies.
And yes, you have to move very fast. It is perfectly doable, though. I succeed all the time when I run IGE with my fleet.
The workers assimilating the officers are triggered by proximity and aggro in the rooms while the whole optional is on a 15 minute timer. There is no margin for error at all.
Some dedicated people actually made a very nice map that shows all the trigger lines (red) among other things.
Never cross any of those lines unless you're about to charge into the next room.
Here's a vid of on of our runs, so you can get an idea on how to do it.