So... got a plan to retake that chamber and deanimate everything in it? Because you're sure as hell going to need to if you want to see FPS above 10 again.
Before digging the spire my FPS was 2. Now it's 1. I haven't really noticed much of a change.
Regarding the above spoiler:
So the demons were reanimated by the necromancer, correct? Doesn't that mean your FPS is still awful? (Although of course it probably was already.)
Are you considering obsidianizing the battleground, undead and all? It's certainly close enough to the magma. In 0.40.xx, you'd be able to just melt the zombs with magma, but 0.34.11...
Awesome fort, by the way. Definitely an inspiration to anyone who wants to make fully-developed megaforts. I don't think I could take the FPS
It's the one downside of Megafortness, to be sure. I might one day just go through a list of all the things I can do to improve FPS - I once managed to make the Fort go to 3 FPS, it was like light speeds compared to what I normally experienced
I won't be obsidianizing the battleground, or collapsing anything on them. The corpses and the necromancer are very valuable, there are also FB corpses in their number which I would preferably like to see relocated to HFS. Worst case scenario I'll flush them into HFS with a flood or just try and get some marksdwarves on the right side of the fortifications and shoot them to pieces, but that's a last resort. I have to be very careful with digging around that area, it sits beneath a cavern lake and I don't want to give the clowns access to the cavern world.
Judging from the poll results and how things are going, Necromancer Kogan and his undead factory can be left alone in the spire as long as he keeps the clowns out. The #1 priority is now getting a strike team onto the ground to establish a beachhead for the colony.
Silentthunders will finally get to deploy her secret soldiers; the werecivets are readying for battle.
*EDIT
Missed one of your questions:
As far as I can tell, no demons were reanimated. They weren't all inorganic but as far as I can tell either all organic demon corpses were destroyed in the fires or there is something stopping demon corpses from being resurrected much in the same way that werebeast limbs will not resurrect and create clones of werebeasts anymore.