I traded an iron fly M3 & unhedged M3 (100 point wings) on SPX the last 6 months and it pretty much sailed through the period from Dec to March. I don´t remember much stress or drawdowns. The set-up was very similar to Jim Riggio´s Kevlar trade plan (you can see how good his results were in this period with minimal adjustments/drawdowns). Now that I have OV backtesting and run a similar set-up on RUT I see why a lot of much more experienced traders had problems trading the small cap index, i.e., the move down and back-up spanned about 46% versus 25% for the RUT and SPX respectively. Is this period an anomaly? Otherwise I don´t see why you should take the risk on RUT as the BF premiums don´t compensate for the extra volatility. Looking back through historical data I can´t find a period where it was advantageous to trade RUT vs SPX.