I'm actually quite happy with the performance of the game.
I haven't played it extensively yet, but my computer, hardly a monster, copes quite well.
Resolution: 1900x1200
Antialaising x 2
Model detail: high
Building detail: very low
Land detail: low
Forest Detail: very low
Visual effects: medium
Damage decals: medium
Building amount: low
land shading: medium
Buildings, grass, roads all on
I'm getting 21-30 fps over land, anything from 35 fps and more over water. (And how gorgeous does that water look?!! Wow!)
Machine specs:
Intel dual core 6850
Radeon 5870
4 gigs ram
windows 7
I think this game (sorry, sim) is going to rock, once a few niggles are sorted out.