Cost of carry gives SP a directional bias that doesn't exist with SPX. But, then again, SPX options should be on a synthetic future. You're right, it shouldn't matter. My mistake.
Another one is cash settlement method for SPX which might work like kind of lottery on expiration day.
The margin requirement for SPX is going to come down a lot on April 2nd, see http://elitetrader.com/vb/showthread.php?s=&threadid=78820
Gentlemen If you prefer risk against potencial great profit SPY options are better as es,spx,oex SPY can take low price in the money and they are more liquid with low bid ask spread You can compare 10 spy at 2 with one spx at 20 In first case transaction expense would more high ,in second in most case spread worster ,alsov with calculation of quantity 10 SPY * 0.05 spread = 0.5 ,it is not the each case by one spx at 20 Your respectfully Example SXZDT c1400 28.50-30 today by spy 1412.30 SXZDB c1410 20.90-22.90 today by SPX 1411.08 SFBDJ c140 2.90-2.95 today by spy 140.94 Last is more in the money ,potencial risk lower ...