I recently tried to boost my performance with some Mods. The two I used are

this High Resolution Foliage mod: http://www.crymod.com/filebase.php?fileid=4471&lim=10

And this GTS250 config (since a 250 is around the same speed as a 5770) http://www.crymod.com/filebase.php?fileid=4977&lim=0

I now get gameplay such as this though. The surface and mountains have a non detailed gradient-like look to this as seen in this screenshot(yes, I have the steam version...:

http://img696.imageshack.us/img696/9214/crysis2010112918522942.png

Ideas?

Also, I did use the ultimate nano suit mod as well: http://www.crymod.com/filebase.php?fileid=4600&lim=20

You might be better off asking this on CryMod.