Mark --- Found this thread over at AVSIM. You may have to register to read it if you are not already a member.

http://forum.avsim.net/topic/374015-how-much-ram-for-fsx-on-win7-x64-in-a-sandy-bridge-setup/

Here's one reply though:

"Thought I would add a quote from NickN's article on Setting Up FSX and Tuning It:  "FSX is a 32bit application and as such even when run in a 64bit operating system memory amounts greater than 4GB will be of little use to FSX directly, however, when applied with a 64bit OS and i7 FSX SP2 (or RTM/SP1 with edited fsx.exe files) will be allowed access to a full 4GB with other processes and applications running along side having access to more (over and above). Therefore 6GB (3x2GB) i7 systems as addons and aircraft become more complicated will benefit FSX on a 64bit OS. If you switch to i7 you are far better off on 3x2GB than 3x1GB in system memory.""

Nick's FSX tuning guide can be found here:

http://www.simforums.com/forums/topic29041.html

It's the FSX Bible so to speak.

Bruce