I just came from the IC Marketplace, and boy are my eyes tired. That place moves somewhat like it is drunk, and this is in windowed mode. Oblivion has never run this sluggishly for me on this Core2Duo 3.0 ghz 4.0 ram. ATI HD4890 is set in Catalyst to let the program handle all graphics settings. Something in this list must be the culprit. At least four of these mods have special uninstall instructions, so they can't be deactivated on the fly. What catches your eye as the most suspect?

00 Oblivion.esm
01 DLCShiveringIsles.esp
02 Oblivion Graphics Extender Support.esp [Version 0.42]
03 DLCHorseArmor.esp
04 DLCOrrery.esp
05 DLCVileLair.esp
06 DLCMehrunesRazor.esp
07 DLCSpellTomes.esp
08 DLCThievesDen.esp
09 DLCFrostcrag.esp
0A Knights.esp
0B Duke Patricks - Combat Archery.esp [Version 5.5.5]
0C Duke Patricks - Melee Combat NO RECOIL.esp [Version 5.4]
0D GalerionLeveling-v11.esp
0E GalerionSlowerLeveling-v10.esp
++ bgHighElfSeamReducerFixEV.esp
0F Bashed Patch, 0.esp
10 BOO_BulletTime.esp