Subject: Re: OT: SPY vs SPX options and IV
Am I missing something,

Could it be that SPY pays a dividend and SPX does not?
The other party which is making the option quotes is a big player in the Goldman Sachs league. You can be pretty sure that they have figured it out right.



I'm not sure why close data could be screwy,

I regularly see wild option quotes when the market is closed. Not always, but often enough. Usually what I'll see is a very large spread--which tightens up when the market opens.