The (fan-made?) extra simulator missions in Freespace: Silent Threat seem pretty good overall. I have now finished like five of them.
I am unsure if they will get increasingly difficult or longer. The ones so far haven't been that complicated missions, mainly about destroying a bunch of enemies with your wingmen... but I actually like that. They seem quite short too, so if you fail, you won't have to wait 20 minutes for it to happen, over and over again.
A couple of them felt maddeningly hard (at Insane level) at first, like I think it was the Crippler mission where there came like four or five enemy waves at a rather fast rate, and they'd be shooting at you from everywhere and your wingmen would drop like flies and and and...
My solution was to change everyone to Ursa bombers (and one to a Medusa I think, a lighter bomber which also has an autoturret), and fly a bit farther away from the enemies, telling wingmen to form on my wing. Then when the enemies start to appear, wait until they get closer and tell your wingmen to engage.
While the Ursa bombers are slow, they are quite effective against enemy fighters if you have several wingmen around you, as all your autoturrets will fire constant concentrated fire on enemies, and they will drop one by one even if they are zipping around you.
The first enemy wave had remained near the bigger enemy ships you were also supposed to destroy, so when all the other enemy waves are dead, just head towards them and tell wingmen to engage. You can destroy rest of them together now that there aren't several enemy waves on your tail at the same time anymore.
Then if not done already, destroy the two enemy turrets too (= the bonus objective), and you are done.