EVGA Cant help - can you? (Video/OS Issue)

Ok, I have a REAL strange problem, probably just my crap luck or something, but I have some serious issues with my video cards in 3D environments (gaming) in Vista Business OS. It starts out almost unnoticable, then within a couple minutes gets so bad I cant play. It is like a stutter that gets worse and worse, barely noticable at first, then gets so bad I would prefer lag over this. While it is doing this I never lose FPS, they stay consistent. When I FRAPS the video, it plays back solid and without the stutter and visual impairment I see when I am in game. The video recording is flawless.

First lets start out with what hardware I have:
Manufacturer: Antec P180B Case/EVGA 122-CK-NF68 nForce 680i Mobo/Thermaltake 850w Toughpower Modular PSU
Processor: Intel E6600 Dual Core 2 Duo 2.4Ghz/Zalman CNPS9500LED HS&F
Memory: 4GB OCZ DDR2 PC2-6400 REAPER Enhanced Bandwidth
Hard Drive: (1) 74GB WD Raptor, (4) 300GB WD SATA, (1) 500GB eSATA, (1) 250GB IDE
Video Card: (2) EVGA 8800GTS KO 640MB in SLI
Monitor: HANNS-G 28" 3ms Widescreen 1920x1600 HDMI 1080P
Sound Card: X-Fi Fatal1ty Champion Platinum Series w/64MB X-RAM
Speakers/Headphones: Logitech z-5300e 5.1 Surround 280w & Razer Baracuda HP-1 Headphones
Keyboard: Razer Tarantula Gaming Keyboard
Mouse: Razer Lachesis 4000dpi Laser Gaming Mouse
Mouse Surface: Razer eXactMat Game Pad
Operating System: XP 64-bit (Current OS)


OK, now that you know the hardware, here is what I have done to troubleshoot the problem:

I reloaded the OS to Vista with one video card in, one hard drive (the 74GB Raptor) active, 2GB of RAM, and the sound card in. Once I loaded it up, did all updates, drivers, everything, I then loaded the games (Halo PC and Crysis). The stutter occured almost immediately in both games. 2D environment was perfect, Photoshop was perfect, even things like Camtasia, Fraps, Vegas Video and such were perfect, but 3D games were immediate issues.

So I changed out video cards with the other one - same exact results.

So I placed in both video cards, put them in SLI and got the same results.

I repeated the above processes by reloading OS with the second video card, same results.

I repeated the same processes above but used my BFG 7950 video card instead - No problems (though it could not handle Crysis as well or do DX10, it still ran it on the settings it was capable of), I then installed both 7950's and ran SLI, still ran strong, no issues.

I repeated the same initial process, but instead loaded XP Pro. No issues with the 8800's, single or in SLI. The machine ran Crysis on HIGH settings on everything without a problem.

I dumped XP Pro, went to XP 64, same install processes, no issues at all.

I went back to Vista OS, did the same install from scratch - stutter came back in 3D. I even worked with the nVidia SLI rendering options for Crysis and Halo PC to see if adjustments there helped such as split screen processing, etc. Nothing seemed to help, nothing made a difference.

According to nVidia and EVGA there should be no problems with the Vista drivers for these 8800's. EVGA says that they do not have anyone else having this problem with these 8800's in Vista and I seem to be a unique case. These cards also are 1 serial number away from each other, so they are from the same batch. EVGA is stummped as to my issue and how to resolve it.

I spent a lot of $$ to get dual cards like this so I could enjoy DX10 in all of its overated glory, but am forced to run these in XP for now because nothing seems to work in Vista.

I have an old Socket 939 board (Asus A8N32-SLI Deluxe) I have considered trying to set up just to see if it is the cards or the mobo (seems to be the only two options right now that could be wrong I think), but have not had the time to set up that old system again to test these cards on that board in Vista. I have all the parts to this board (4200+ X2, 4GB DDR RAM, Audigy ZS, 600w Silverstone PSU, HDD, etc - no case though, any way to run this set up w/o a case just to test these 8800 cards?).

Do you think I should consider doing this?

Would this help me eliminate whether it is mobo or video cards?

Could it be drivers in conjunction with video cards on that mobo?

Anyone?