I don't recommend quad sli for any1, its driver dependant...grab another 260 GTX...it would be almost as fast as 1 295 GTX with out the extra price tag.
285(280) tri > 295 GTX quad > 285(280) GTX sli > GTX295 GTX > 260 GTX sli
But the 260 GTX sli would be your best Price/Performance ratio.
What kills the 295 GTX is the low Vram count for such a high end card (compared to the 100$ cheaper 4870 X2 which is 6 months older) and the small bus width of 448 bits I believe.
As a single GPU the 295 GTX is just a hybrid of 260 GTX and 280 GTX featuring 240 SP.