But dual GX2 has 4-gpu as compared to the 3 in the Tri-SLi. And Tri-SLi doesn't seem to scale very well in the only game that needs more than 1 (or 2) GPU, Crysis.
The thing with the GTX is you can find factory OC cards like EVGA 770Mhz, the max on the GX2 is 700Mhz I think. So in games that don't scale well the GTX will be better.
I think this 3-way technology is still new and, yet to make solid performances in games.
In fact, I don't think any games have true support for 3 GPUs...