It depends.
In the new version, specifically in 40.08 w/dfHack, I only use:
-pocket world (17x17)
-zero rain
-40 drain (with above means 99% of the world is rocky wasteland, meaning
no trees,
no wild plants, no surface sapling growth, etc)
-3x2 embark size
-one cavern
-5000+ mineral scarcity
-very shallow world, typically <20 Z-levels from embark to magma sea, making volcanoes often unnecessary.
-no divine metals (useless in fortress mode)
-no savagery, no evil, no werecreatures, no vampires, no necromancers, no night creatures, no titans, no megabeasts, no semi-megabeasts
-2 demon types
-two civs (with several thousand goblins, the TRUE dwarven enemy)
-3 sites or less
-historical figures culled / don't reveal all historical events.
->90% of the world is the same elevation
-no rivers (no rain)
-max 40 dwarves
-[FLIER] fix
So, for me currently, my FPS in a 15 year old fort with a surface embark volcano is >400.
In a 257x257, 5k+ history, 100 rain, 100 drain, 100 civs, 100 sites, 100 mineral scarcity, 50+ demon types, broken fliers, three caverns, super dense flora, savage fauna, evil ground, evil rain, evil clouds, titans, megabeasts, werecreatures, vampires, necromancers, massive rivers, waterfalls, multiple rivers, 5x5 embark size, etc, I could see getting down into the single FPS digits quite quickly.