Someone Somewhere :
No, the same stuff needs to be in each VRAM, so it'll still act as 2GB.
+1
Thats also the reason to be wary of VRAM capacities in dual GPU cards like the 690. Says 4GB on the front, but it only has 2GB of effective VRAM since each GPU has 2GB, its not a shared pool.
If that's the case, what are the benefits of an sli setup if it doesnt combine vram?