SLI NVIDIA 2 monitors 4 windows lag

Hi, I've spent over 15hrs toying around and tweaking this multiboxing software and managed to solve only good sinchronization (by setting mouse following to CENTER, instead of default one and insetad of SCALED TO FIT), but failed completely at making 4 copies of Diablo running without lagging.
3 windows run at 40-60fps, but when you add 4th instance it drops to 2-6fps. And i figured out that it's NOT the problem with CPU, RAM or GPU. After monitoring all of them closely in different setups i came to this conclusion, that i miss something really small, but improtant in setting up correctly.

I have 16gb RAM, 2700k processor, ultra-top gaming Asus dual-bios MB with constant 4.4Ggz, SSD top drive and SLI Nvidias on 30" and 24" monitors.

Each copy of the game runs on it's own separate core and in hyperthreading mode.

I've tried gazillion combinations of window layouts, using one and two monitors, played around with CPU wizzard (obv for me each core for it's own copy is best). My RAM is not even close to beeing used up, my CPU is used less then third of it's potential at all times, my GPUs is around 56-78% of usage. I've tried SLI, tried turning it off, tried disabling second monitor etc, wish i could use Nvidia Physx for 1 videocard, unfortunately Diablo has it's own, which suck balls. Also tried overclocking my GPUz, but no increase in fps lol.

Well, basically looking for any solid super-advanced tricks, besides those that i found.

Thanks for help.

[MiRai]

SLI Nvidias on 30" and 24" monitors.

So what video card are you using? You don't say what resolution you're attempting to run your games at either?

3 windows run at 40-60fps, but when you add 4th instance it drops to 2-6fps

This is almost an exact indication that you're overloading your GPUs.

And, as we tell everyone, please share your config.