Originally Posted by Rollo
You would do your system far more benefit buying a Sandy Bridge or highly clocked 1366 motherboard than any graphics move you can make.
Your graphics are great for the GD235HZ monitor, there is no need for more than 1.5GB VRAM for 19X10. Likewise, there is no need for 4 GPUs for 19X10, even with 3d Vision.
Your SLi scaling is being limited by the AMD CPU. I say this as someone with a 3.4GHz Phenom II in one rig, and a 3.4 GHz i7 in the other, and first hand experience with the CPU holding back the variety of GTX5XX SLi rigs I've used in that rig.
I think I saw that he's running 3 displays, in which case you could definitely see the benefit moving to more graphics horsepower.
Also as a general note... dual-core cards don't count as using SLI... I could use a 295 / 590 on my system and even though it's a P45 chipset it will work.