In 2013 I was looking at GOOG 450$ -ATH and thought the price was not good for a long so sold it. The price had nearly doubled in less than two years. Now I know that price and ATH's should not dictate how I invest. If SPX breaks I would look for a better entry around the 2250 area (in the very short term) before considering it overbought. Until then I think a good short will happen on the intraday basis (pull-back) only. I only say this because it's been over a year since SPX has been at this level. The SPX generally gains about 8% per yearover 90 years of data. There could be about a 12% potential upside move to consider if you look only at price.