There are some ways to keep high fps
- smaller map size (default is 4x4 but you can still make decent enough fortress with 2x2 , and additionally it can be more challenging too as invaders are then more dangerous as they don't have to travel as long before reaching your walls)
- no more than 100 dwarves , apparently 100 is the minimum to have all the DF features according to wiki, but if you don't care about fortress evolving into a city or metropolis (that requires apparently 120 and 140 pop), 80 is even better.
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atom smasher (as simple as making a 3x3 raising bridge in a 3x3 room closed by a door and controlled by a lever) is a must to get rid of the thousand of useless objects (oh those very competent fisherdwarves and the tons of mussel shells garbage resulting and those gobs invasions meeting your competent dwarven warriors) that will soon be part of your fortress
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quantum stockpiles with a minecart stop are a must so when an ai needs an item, it's all in the same place so no pathfinding through the whole fort to get all the items it needs) , they're not as easy to setup as an atom smasher but once you have done them once or twice it's easy to redo them
- Setup large zone of
traffic set to Restricted where no dwarf has any business to go over the map, will spare pathfinding calculations.
also make sure there is no door with "Keep tightly closed" enabled to prevent animals to go through them, it's a great way to heavily destroy your framerate
Cut trees regularly, this to prevent dwarves to accidentally (often when they are in a fight against an opponent or running after an animal) climbing on top of a tree and staying there without knowing how to get back, they can hammer badly the framerate (especially if they're getting a mood or are part of a squad you sent to a raid)
Apparently playing on young world can help too due to the game having then less historical figure/items to keep track of
I've been able on an old potatoe to run a 20 years old fortress in one of the 44.xx releases without framerate dropping below 50 in those conditions.
Sure i would love to not be forced to use all those tricks and limiting then what can be done in DF in order to keep the game comfortably playable enough for me , but considering low fps means everything even the simplest of task takes forever to be done and make it so incredibly boring, those tricks are currently the only way i found to no stop playing the recent versions of DF as i didn't needed that much self imposed limitations in pre-DF2014.