congo, that is an incorrect statement, back when I was on my G4 Ti4800SE i would get like 5 FPS with sliders maxed and lots of clouds and rain.... I then up graded from 512MB PC2100 to 1024MB of PC3200 and my fps jumped to 15 with the same settings and the same amount of weather.... It makes a pretty large difference
Swanny, it may have worked in your case, I suspect because your system was overloaded with background programs.
Flight Sim only uses around 120 mb of ram, so I can't see the biggy about Ram. I can pull one of my 512mb sticks out and it doesnt seem to make any difference with only 512mb ram. I have very little running in the background though. Also, my new P4 rig only has 512mb of ram and it gets around the same FPS as my AMD PC with 1024mb, I've tried both PC's with different RAM combinations using 512mb of DDR PC3200, 512mb DDR PC2700, and 1024mb DDR PC2700.
Where the extra RAM helps, is if you are processing huge textures for example..... so if you enable the MASSIVE texture sizes in FS, Sure it will use available RAM, but your BIOS must be setup to enable huge textures in graphics as well.

Mainboard: Asus P5K-Premium, CPU=Intel E6850 @ x8x450fsb 3.6ghz, RAM: 4gb PC8500 Team Dark, Video: NV8800GT, HDD: 2x1Tb Samsung F3 RAID-0 + 1Tb F3, PSU: Antec 550 Basiq, OS: Win7x64, Display: 24&