Adding 3rd video card = *worse* performance? :(

I'm not sure if this is a Vista issue, an nVidia driver issue or just me. I'm trying to 5 box on a Vista x64 Q6600 machine using 3 monitors and either 2 or 3 video cards:
- Main WoW window (1600x1200) on monitor 1 driven by an 8800 GTX
- 2 clone windows (800x600) on monitor 2 driven by 1 2nd 8800 GTX
- 2 clone windows (800x600) on monitor 3 driven by *either* an 8800 GT or sharing the 2nd GTX

I know that WoW isn't a very graphically intensive game, especially since I have all of the bells and whistles turned off on the clone windows. Still I thought that using 3 cards would be at worst overkill. Instead it seems to hurt my framerate badly. My observations:
1) If I drive my 3rd monitor with the 8800 GT (3 GPUs) I get 30 fps on my main window.
2) If I drive both monitors 2 and 3 with the 2nd GTX (GT is unused) I get 45 fps on my main window.
3) If I drag all 5 windows onto my main monitor I get a steady 60 fps on my main window.

I'm not exactly sure what to make of this. Bus contention? Driver issue? I'm curious to know if others see the same thing, and if so if you ever found a fix. It looks like an easy partial fix is to throw my brand new 8800 GT in the trash and just run 2 gpus, but I really want to get back to a smooth 60 fps on my main. Any suggestions would be great.

I have head from a friend that having a 3rd video card is not worth it, you will see barely a increase in performance, and sometimes can even cause issues.
I just thought I would throw that in, I cannot really help you with your problem.

Yeah, I'm going to pull the 3rd video card since I apparently don't need it, and I'd rather have it out for power and airflow reasons. I'm hoping to get 5 widows going on 1 machine with 60 fps on my main though. Right now I'm only managing 45ish, and I'm worried it will dip further in Outland.

I could also bite the bullet and use > 1 box, but that makes things more complicated.

You WILL dip in Zangarmarsh. I dunno what it is but I got a drop in rates riding out of Cen Expedition's north bridge and was reminded of another post here months ago saying "They did something graphics-wise in outland, especially in Zangarmarsh..." and I though "christ they weren't kidding" :p Wasn't anything MAJOR but it was noticeableish; best way to fix yer rates is to not JUST set alts to maxfpsbk low, but set maxfps low too even if they never come up front; for some reason that DOES seem to have an effect on the remaining WoWs. I leave all 3 of mine at normal fps, I avg 20-40...I set the 2 alts to maxfps 30 to 35(usually 32 or 33), and my main gets back up to 64fps easily.

The third card is probably causing a bus bandwidth issue. I'm not sure of anything to test that other than looking at the your motherboard chipset and how much data your video cards put onto the bus vs bridge/chipset performance.

You'll probably find that the second and third PCI Express slots on your motherboard are not x16 electrically.

I've got a board with three PCI Express x16 connectors, but they are electrical x16, x8 and x4. If I install two graphics cards in the x16 and x8 slots, they both run at x8.

[quote='Sarduci',index.php?page=Thread&postID=42038 #post42038]The third card is probably causing a bus bandwidth issue. I'm not sure of anything to test that other than looking at the your motherboard chipset and how much data your video cards put onto the bus vs bridge/chipset performance.[/quote]

[quote='Ozbert',index.php?page=Thread&postID=42317# post42317]You'll probably find that the second and third PCI Express slots on your motherboard are not x16 electrically.

I've got a board with three PCI Express x16 connectors, but they are electrical x16, x8 and x4. If I install two graphics cards in the x16 and x8 slots, they both run at x8.[/quote]

Interesting. My mobo is an EVGA [url='http://www.evga.com/products/moreInfo.asp?pn=122-CK-NF68-A1']nForce 680i SLI 775 A1[/url]. The manual claims, "Two full-bandwidth 16-lane PCI Express links ensure maximum graphics performance for next-generation GPUs and games. This feature offers twice the PCI Express bandwidth of x8 SLI solutions." So it makes sense that the 3rd card was a disaster.

I still get some degredation in perf from the 2nd card. I actually do better if I run monitor 2 (clones 2 and 3) off the same GTX as my main monitor, although it starts to run a little hot (81C today). I've played around with a 2 computer setup using Octopus and an old P4. I may eventually have to bite the bullet give up on single physical boxing. /cry