So after a long while, I finally got a game in, but ended up running a different list after having a change of heart about the sort of army I want to run.
~My list~
Destroyer Lord with Weave and Res. Orb
10 Immortals with Gauss Blasters
10 Immortals with Tesla Carbines
5 Destroyers, who went around accompanied by the Lord
Monolith
Annihilation Barge
~His List~ (I don't know the details perfectly)
Librarian with an ability that allowed him to shoot often with low ap
A 9-man Tactical Squad without special weapons to which the Librarian was attached
5 Assault Marines w/ Power Fist
5 Terminators w/ Assault Cannon
10 man Tactical squad, divided into two teams, had a missile launcher, might have had a plasma gun as well
Land Raider, whichever variant has hurricane bolters and twin-linked Assault Cannons; hull-mounted Multi-melta
My opponent is pretty new to 40K, so I didn't take the result of the game to be terribly indicative of how my list will function at a higher level. Our table was pretty claustrophobic (4x2 feet), and we deployed diagonally so there wasn't much for me to do but just set up in my tiny corner and wait for him. Mini batrep, I kept my Gauss Immortals in reserve to give me some space in my deployment zone/maybe ensure the survival of my anti-Land Raider firepower and used the Monolith in combination with my Destroyers to remove most of his threats as they came down the pike. The Annihilation Barge commanded a lot of my opponent's attention, and so I was able to use it to lure the Terminators out of center field, slowing them down behind the rest of the army and buying me time to eliminate everything else before having to deal with them. Ended up losing a little under a third of my army, and that was because I consented to throw the Lord in with his remaining Terminators. All in all, I lost the Annihilation Barge, the Lord, and about half the unit of Tesla Immortals.
Not the most telling contest given my opponent's inexperience, his (presumably?) subpar army list, and the unusually cramped game conditions, but I was curious about how easily this army of mine might be overrun by common CC threats, and also if my Destroyer-chaperone (Lord taking point with his superior armor save) wouldn't be outperformed by maybe an Overlord and some Crypteks. Mostly I'm drawn to their Haywire weapon, since that would give my two troop choices additional anti-tank capabilities, but a lot of my points are tied up in the Destroyers and it's comfortable giving them added survivability. Biggest thing that's bugging me right now is I really don't know what the common/nastiest threats from the other codices anymore.