call of duty 4 graphics drop with 9800 gx2 ??

Hi I have upgraded from an overclocked BFG 8800gts to a 9800gx2 when I first put it in i noticed no real FPS gain.I reinstalled drivers and had a good increase in performance. Today now struggle to get a constant 125 fps at lower resolutions 1200 x 1024 .I have monitor which is 1900 x 1200 res.surely I should be able to achieve this on my system?I have had to turn off some graphics settings to get a steady 125 FPS which is what I am looking for.Any ideas?? I got 16800 score on pcmark 3D 06. so I think the card is installed o.k

QX9650 YORKFIELD PROCESSOR running at 3.1 G
ASUS MAXIMUS FORMULA motherboard
BFG 9800 GX2 graphics
ocz 8 GB PC2-6400 DUAL CH. VISTA GOLD SERIES RAM
XFI FATAL1TY SOUND CARD
RAPTOR 150 G 10 000 RPM HD + 500G HITACHI DESKSTAR
ANTEC NINE HUNDRED GAMING CASE
800 W POWER SUPPLY
64 BIT VISTA ULTIMATE