I have an i5-2500k@4.3 w/16gb ram,2ssd (1 os, 1swtor) w/sli 980gtx sc and I play at 1440p.
I average around 80-100fps in open world and in 8man operations and pvp my fps is around 18-25 when in combat with other players. I will say SLI had almost zero impact on my fps as the game is hugely CPU dependent.
I would honestly recommend you invest in a watercooled setup for your CPU and overclock it. I use the kraken x61. You will see a larger fps increase than just adding another 970.