My take on Opex is that it's a complete mixed bag. Generally speaking, each stock is guided into a price based on options activity, and market sectors do not move consistently at that point.
FAS, which is an index, sees volatility on those days because of all the underlyings.
In my scenario, GS may go up because the calls out there are big money. FITB may go down because of the puts. So Indexes can literally be the WORST play of the day on OpEx. Individual stocks can be a better play.
Any other time of the month, we tend to see sector moves (especially in financials!) and they can be more readily timed.