The sea is ruining my framerate, is there anything I can do to increase my FPS?
I've got a nice little coastal fort going but even on a fairly small embark spot it's killing my frame rate.
If I built floor over the sea with stone, would that be likely to increase the frame rate as the game would no longer have to simulate waves?
I don't believe this will help. Even if covering the ocean with floor prevents the waves from being displayed, the simulation will still calculate them (the DF wiki says waves "seem to move independently of constructed tiles like walls and floors.").
Hopefully you can find something on the framerate wiki page that helps.