Only ship I would consider bothering with turrets would be the cutter.
As for conda I would go gimballed, OK maybe turrets on the smaller hardpoints.
The corvette, putting turrets on that is just shameful.
Best weapon loadout I have found for corvette has been two class 4 fixed beam, a gimballed class 3 beam, and gimballed cannons on the rest.
The slf as Lori says can easily kill off most wingmen, but their true value isn't their significant deadlines, but getting fire off you, distracting a targets wingmen and in most cases killing them outright.
Rank a pilot past expert and it should be able to take on any ship.
My method for engaging, say a high ranking conda in a wing with two FAS's or even gunships would be to send the slf at one of them, I would kill the other in the vette and in most cases even before the conda can react, my target is gone, and my slf has either nearly killed the other so I can take on the main target or join the slf, depending on targets rank and other situational circumstances.
Only time I loose an slf is if it gets swamped by multiple targets.
But that's mostly only an issue in cz's.