hardware question

EDIT: ok so after reading all the comments, and thank you all so VERY much, i understand that i can feasibly put a second graphics card in my computer.

now based off what i am understanding, if i were to go with the second 970s rout, i would have a faster final render time but the preview render feature (some sort of real time render coolness) would still tap out at the 2 gigs level (if a preview scene needs more then 2 gigs of ram on the gpu it says "error" )
though the "best" solution seems to be upgrade my motherboard, and get a new gpu

thank you for your help


so general question to all:
i am thinking about getting a second gtx 970 Nvidia graphics card.
i have a Sabertooth 58x motherboard from 2010
does anyone know if this motherboard can support an SLI GTX 970?

to make my scenes faster and more detailed i need more cuda and GPU mem and the sli option seemed most cost effective