NVIDIA will soon bring the compatibility of the GTX 670 with technology 4 - way SLI via an update of drivers.
The GeForce GTX 670 has two bridges SLI on the PCB, this one that suggested that the 4 - way SLI was possible but apparently, according to the PC Perspective website, is currently not the case, 3 - way SLI is operational.
The GPU GK104 GTX 670 being a very close variation of the GTX 680 and the PCB allowing two SLI bridges, there is no which would prevent this multi-GPU technology to function. After contacting officials in NVIDIA our colleagues have learned that 4 - way SLI would be soon supported with a next update of drivers.
When we see that a two GTX 670 SLI is only 2% less efficient and 20% less expensive than a GeForce GTX 690 with a consumption of lower energy, 4 - way SLI is therefore be a tempting solution, if drivers follow course. Case to follow so.