The 2003 low for $SPX stands at 768.63. ES is currently trading at a discount of -1 to the cash index. Hence, keep your eyes glued on 767-ish.
The worst case scenario for the bulls is to end the day below the 2003 low. The worst case scenario for the bears is to retest the 2003 low too early and risk a quick reversal.
Just covered since my crystal ball is indicating that we might be reversing and heading up. Hmm, better be safe than sorry though.