I haven't played since the GUI release, but in the past you definitely had to set a fortress population limit to prevent FPS death.

Also, assuming DFhack still exists, you can try using it to clean up the messes and splatter which can bring it down a decent amount.

Fortress design may also have an impact on FPS from pathfinding according to some, but I had limited success in improving FPS through more optimized pathfinding designs, and the number of entities on the map still seemed like the biggest factor.