Lots of items? Lots of animals? Large embark size? Large world size? Long history? Messing with fluids?
Graphics settings will have a minimal (if any) effect on FPS. I'd be surprised if your operating system was a major factor.
Are you playing on a different computer?
Same laptop, different OS. Same version of Masterwork.
It's a 2x2 embark, medium world size, I start at about year 8. I have learned not to break into the caverns or else suffer FPS death early.
I just can't seem to isolate anything specific as the "cause" of the high FPS. It just starts creeping up as the number of dwarves starts to increase. I can hit the clean all and clean owned in DFhack and that will increase the FPS back up for a short time but then it starts to fall again.
Dwarves is the worst, warlock is the best ... so I keep thinking it's something related to pathing and fort design.