In real world in terms of buying I have been getting between the mid and 20% below the mid, excellent executions. Expect exiting will be the same. This is over 10 trades or so. So am now a fan of SPX over the SPY options, maybe better executions despite wider quotes and better comms and better taxes. Cheers
I am about .55 all in a side at ET, same as SPY or IBM. I do get a discount as high volume, but think std is .65.