Design a way for your dwarves to nearly never be in line of sight of each other.
as apparently this create a lots of checks that may end to be most CPU intensive and when lots of dwarves are in each other line of sight it can get nasty and become one of the big reason of performance issue :
http://www.bay12forums.com/smf/index.php?topic=180561.0So i imagine a good use of burrows so you can separate the dwarves and keep only a certain amount of dwarves in specific areas out of sight from the other groups will keep those problems relaitvely in check, but that means probably forget about taverns, temples, other social area etc...
Maybe a workaround to that is to build each floor of your fortress as independant (using burrow) from each other, so if you only have a limited amount of dwarves in a floor, even having taverns, temples, etc... may not get so many dwarves into them, limiting then the amount of line of sight checks.
Also, while said thread mention pathfinding is not a major cause of FPS death, there are some known problems (a creature stuck on a tree, or stuck on anything it is hopelessly trying to path to your fort but can't, a dwarf getting a mood while stuck on top of a wall without stairs ...) that can also destroy your fps.
In the case of caverns, walling them off from your fort can help as creatures aren't supposed to be able to check pathfinding through walls.
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