Quote -  

Quote - I ran out of texture slots before I ran out of memory. And you can reduce texture size, remapping props and figures is not as easy. I gave you the limitation of using a GTX580, if you think that is not a problem in your case, then all is fine. I just want you to be aware of it before you buy your second video card

 

 

But I already have two 3GB GTX 580s.

Then go ahead with that. If you do run into the texture slot problem you can always consider getting a 600 series for larger scenes. But do get that extra videocard (which ever it is) to offload the OS UI to that card to improve your UI responsiveness.