Hi, using the Sapphire HD 5750 1GB Vapor-X (its just the normal 5750 just OC'ed), Flying by myself, I get 60 FPS over the channel, 45 over land, and around 30 over London.
I use these settings.
Res. 1600-900
model: high
building: medium
land : high
forest : off
visual effects: medium
textures : high
AA - 1X
epilepsy - off
ssao - off
vsinc - on
damage decals - high
building ammount - high
land shading - medium
grass- off
shadows - off
roads - off
Since you have a better vid card then me, you will be fine using similar or better settings.
Edit. What OS do you have? I heard the CloD doesn't work good with windows XP or other 32 bit OS's.