I just downloaded Desastersofts latest Adof Galland Fighter Ace campaign and I believe it recommended around 8 gigs of ram.
I'm currently using an Asus PT6 motherboard with 3 - DDR3- 1600 2 gig sticks in Triple Channel Memory format. My only problem with the game is a slight terrain stutter flying at treetop level over London, and wonder if 3 - 4 gig sticks would make any difference.
When I check with CPUZ it appears my memory is running around 2100 NB frequency. So I wonder if it would make a difference putting in DDR3-2000 memory instead of DDR3-1600.
Anyway memory is very cheap, much cheaper than buying a 680 4gig video card.
edit I'm using Windows 7 64bit OS
Also remember the operating system memory limitations.