Would an i5 3570K bottle-neck a 2-way SLI GTX 680 and a 2-way SLI GTX 670?
Double-edged answer, so yes and no. For a single-screen gamer, no it wouldn't. If you were to be on a triple-screen, 120Hz setup, then depending on the game yes.
For the most part, the Core i5 3570K is absolutely more than enough. If it's not enough, then a bit of overclocking would definitely push you over the edge and give you that bit extra grunt that the SLI setup would require.
I'm going to guess that you have a single monitor (or TV) setup at 1080p, so if you do, then the CPU is fine.