on a side note if you have the money, it's best to trade SPX options over SPY options because of the 60/40 tax rule benefit which is the same as you get for trading futures i.e. 60% of your gains are taxed at the long term capital gains tax about 20%, vs short term capital gains which can be mid to high 30's, that's a huge difference. 

the caveat is that SPX options cost about 10X more than the equivalent SPY call/put option, therefore you have to have a large enough account to do it.  

for example on the SPY system the call options we've done have been priced between $20 - $40, or $2000 to $4000 each.  The same SPX equivlaent call options would have cost $20,000 to $40,000 each.  and if you are buying 2 contracts for 2nd entries that can be $50 - 80K for two options and of course you have to have capital for systems that overlap on trades.  For the SPY system you would probably need $200K to trade the SPX options whereas with SPY you could do it with a $20K account.  anyway just an FYI. However if you have the capital SPX options are superior because of the tax benefits. The rich trade ES and SPX options, NOT SPY options