Hey Digitised,Have you installed the Far Cry V1.3 Patch?
In case you Haven't try Downloading it from
here.
Just apply the patch and then try running the Game at Higher resolutions.
Also My friend happens to run it at much Higher settings Viz 1600x1200 with every detail set to max and with 6X AA and 16X AF on His ATI Radeon X800XT PE and the game in now way experiences any crash.
Btw Just one more question to you,How much did you exactly pay for the 6800GS from XFX? Is the leadtek Model available? If yes then for what Price as I Seem to have seen it advertised lower than XFX.