Fallout 3 "microstutter" - nothing works

I purchased Fallout 3 from Steam about 3 months ago, and I from the very first player-controlled section of the game, I have noticed the “microstutter” that many people have been discussing over the past year on the various forums. I have not had this problem with any other game. When I run FRAPS, the frame rate is always pegged at 60, yet the game stutters like the frame rate should be dropping 0 every split second. It is so annoying that I actually cannot play the game. Like most people have mentioned, the “microstutter” is most noticeable when strafing around a corner or circle-strafing around something. I should also note that during character interactions and when using VATS, there is no microstutter. Does anyone have any new ideas on how to solve this problem? I have tried the following without any joy:

-iFPSclamp: This doesn’t work and seems to make the game weirdly fast
-The litany of .ini file changes, forcing vsync on or off etc…
-Basic background program/process optimization, setting the priority to “High” and “Real-time”
-Page file and hard drive optimization (defragging ect.)
-Upgrading Vista to SP1 then SP2 then SP3
-Updated all drivers (including bios)
-Disabling onboard sound and putting in a sound card
-Upgrading my RAM from 3 gigs (4 Sticks dual channel) to 4 gigs (2 sticks dual channel)
-Tried running the RAM in dual channel and single channel mode
-Swapping out my current HIS Radeon HD 4870 512 with my old x1950XTX (i.e. not the power supply or the GPU)
-Under-clocking and over-clocking both graphics cards
-Turning on Catalyst AI, then turning it off
-Using ATI Tray Tools to force triple buffering
-Using 3rd party Radeon Drivers (DNA/Omega)
-Setting the refresh rate from 60 to 75 then back again
-Setting the core affinity to one core
-Removing antivirus software
-Got a Razr Salmosa mouse and an XBOX360 usb controller **(by the way, the Razr mouse polling at 500mhtz solved the same kind of micro-stuttering I had with Far Cry 2 oddly enough)

Here are my system specs: (It’s a pretty heavily modified Gateway GM5632e)

-Intel DG33SXG2 motherboard (Intel Schroeder Town board for Gateway systems, also known as a DG33TL or G33 chipset)
-Intel Q6600 @ 2.4ghtz with an Evergreen heat sink/fan combo (never gets above 30c)
-4 Gig 800MHz XMS RAM timed at 5-5-5-12 1.8v, running in dual channel mode
-SoundBlaster Audigy SE with 4 speakers and a sub
-HIS Radeon HD 4870 512mb running at 750 MHz clock/1060 MHz RAM
-2 450 Gig HDDs in RAID 0
-Logitech keyboard, Razr Salmosa mouse
-Vision Tech 19’’ monitor at 75 MHz
-TOPOWER 750 psu w more than enough amperage on the PCIe connector