I've often wondered the same thing myself. I know of a $400M-$500M long/short utility fund that shut down because the head guy woke up one day and decided that oil above $40/barrel was not sustainable. Lost enough $ making bad directional bets that the big investors pulled out and the fund had...
Try switching from "Single Symbol - NOT WEIGHTED" to "Portfolio - BETA WEIGHTED" on the analysis page of tos. You can model SPX with SPY, and anything else you want, on the same P/L graph.
I too have modelled the effect a 10% drop and a huge vix spike on a double (or single) diagonal. The question I have is how wide will the option b/a spreads be in the event of a black swan, and how far from the mid will you be able to get filled.
Thanks
Pete
You might also experiment with wider strikes. Haven't looked into this as much as I would like, but wider strikes on the diagonals seem to lessen the effects of a drop in IV.
Coach;
I seem to recall your mentioning a long while back that you knew someone at a hedge fund who was trading very wide credit spreads, ie 10x100pt spreads instead of 100x10pt spreads. I am curious to know how his positions have fared these last few weeks what steps he has taken to...