need some help from the "Memory gurus" here

hi guys,recently my Alienware mobo. (Asus P4T533-C) P4 3.06, 1gig of PC1066 RDRAM was replaced with an Intel 875PBZ mobo. P4 3.00, 1gig of DDR PC3200 ram. also, the WD 60GB 7200RPM with 8MB cache buffer HD was replaced with the Seagate 80GB 7200RPM 8MB cache HD. 9800XT, Audigy2 ZS & all other hardware is the same. my performance in FS9 has gone downhill with this new setup. for example, with the Asus mobo./RDRAM setup when flying at cruise altitude in the default 747 on top of a solid overcast my lowest fps was 10-12. now with the Intel 875 mobo./DDR setup the same FS scenario listed above my lowest fps is now in the single digits...4-9. the popping/filling in of the terrain textures now is larger and slower. also,the A/C textures "pop" in as well. this Was Not happening with Asus/RDRam setup. All FS in game settings and ATI control panel settings are the same. Full "stock" FS9 install with Bill Molony's "Atlanta Skyline, Turner Field, Atlanta Airport Addon" installed on both systems. running WinXP Pro SP1, DX9.0b, latest mobo./chipset drivers, video, sound drivers as well. any help would be appreciated.happy flyin, fm