Make sure you have all drivers updated to the latest version.
Check out this thread here and follow most if not all of the suggestions made in it:
http://forums.eagle.ru/showthread.php?t=68060
(last link courtesy of someone else who posted this before)
Only way to get rid of the three blue lines on Radeon cards is running in DX9 mode instead of DX10, but you might suffer from fps dropping (at least it gives worse fps for me)
You have to set this in the conf.ini in Documents\1C SoftClub\il-2 sturmovik cliffs of dover\conf.ini
Of course defrag your system and shut down unneeded background processes, also disabling windows Aero themes might help.
Added example image of how much of an immersion killer those blue lines are below:
