Yeah. Some tips on these large siege mods:
1. Animal bombs (cages in a room at the side of the corridor sealed with a drawbridge stuffed with tigers linked to a lever. I know, very long.) are very good against hardhitting voidwalkers. They attack the tigers instead of the dwarves, who really cannot afford to get hit by a *glistening voidshard whip*. Be prepared to request for tigers and even dogs every year for this. Tigers > dogs because they take more punishment, therefore reducing cleanup. And it's just the Rule of Cool. Also, don't put them all in one cage. Only one dwarf will be assigned the Cage Large Creature job. I count the war tigers I have, then divide them up in the cages so multiple dwarves will load up the cages. It's faster this way, since this is such a crucial tactic against voidwalkers. Without it, my dwarves fall to pieces against voidwalkers. (since I havent managed to equip everyone with voidshard yet, and also cuz I'm challenging myself not to mine addy.)
2. Sieges like mine drain FPS like crazy. Conserve FPS by atomsmashing stone and clothes. This map of mine is a 3*3. My usual FPS was at 50 ish. The siege was at 10, then 20 when the goblins routed, then 15 when the bog trolls showed up. Then it was at 30 when the dust cleared (all the clothes and miasma etc)
3. Do all your fighting inside instead of meeting them in an open field. The main reason isn't archers, but clean up. Seriously, that stuff drains FPS and you DONT want a hauler walking to the edge of the map to pick up voidwalker shoe. Avoid the caverns unless you really need it. In this fort, I avoided it and this is the fastest fort I've ever had. (although this being the first 3*3 embark, and all the atom smashed stone probably helped. Still, caverns are a drain.)
4. Mid game fatigue was something I suffer from. The fort looks ugly, the migrants suck, the clever designs you thought up to mangle goblins isn't operational, and ambushes are lurking around every corner while your army is still in unskilled peasant and unforged metal bar form. I posted this in the Dwarf fort discussion forum once, and it's advised you just brave through it best you can.
5. During the animal bomb, or even in normal fights, sending 100% of your dwarves into the fray may not be a good idea. Lots of dwarves at once will kill voidwalkers fast, but their AoE death wails will usually affect them all. I usually leave one squad off the fight, so if the frontline fighters are all dizzy and shit from the death wails, these fresh fighters can go in and continue the fight. This is a risky approach, though, since voidwalkers need every dwarf you have to be attacking them so their not doing the same to your dwarves. I noticed this problem in a siege yesterday, all my dwarves dizzy and vulnerable, prompting me to train up a new squad for this reserve tactic. Since all the voidshard whips were lying around, I drafted some farmers into the late lasher squad.
My 3*3 embark has no flux, but lots of minerals. Iron, iovium (small amount) and orichalcum are present. Ferrovanadium is also present, but not in the layers I operate in. Tetrahedrite galena and splaherite is also present, but they goes without saying.