Count mine as a big NO!. mistakenly voted yes
.. With your current monitor. You definitely do not need sli 670's. I'll say Upgrade that first before considering a 670 SLI system. Get a good 120hz monitor, I have SLI 660's, and i know they perform similar to the 580's (single card wise), but i don't know how well they scale compared to each other in SLI. I get very high FPS in graphic intensive games, and I assume you have similar performance as i do. So NO, don't upgrade! "yet", I mean... why fix it if it's not broken?
I know right now you have the extra cash to spend, and if I was you, i would work on balancing the system's performance than only focusing on the Gpu's.
... I had the option of going SLI 670's too, but went with SLI 660's, and i got a extra ram, Better sound card, a new chair, glass desk, speakers (with a 200w sub)
... desk light haha and lots more. There are a lot of stuff's that people don't take serious, but they actually make gaming a whole less stressful on the human body
. Just chill. Wait for the 700 cards to come out.