Here is one test from me showing some trees without fog of war:
v3.5.2:
tileset desert: 128 fps
tileset dark forest: 100 fps
svn(2736):
tileset desert: 97 fps
tileset dark forest: 74 fps
So the tileset seems to make a difference for you, too, both on the old and new version.
For reference, here's what I had to say about it:
FPS decreases massively from 25 to 5 FPS when camera is above forest with tilesets Meadow and Dark Forest; this happens on both current subversion revisions as well as on 3.5.2, and I'm not sure whether it only happens since I upgraded to Ubuntu 11.10 or whether it has always been an issue with my or any GPU. It needs to be tested on other systems, i.e.: please help!
The overall FPS has sligtly improved for me from 3.5.2 to 3.5.3-dev last time I checked. I may have another look at this these days and update this post accordingly.