The ES/SPY on a day-to -day basis is actually less volatile than a 10-year bond, but TLT and IEF have much shallower skews and IV than SPY. But look at the huge trading range for TLT since 2009. It has much bigger swings than SPY, and it's not uncommon for TLT to fall 5-8% in a month whereas that is very rare for SPY. I would seem obvious that one should sell index volatility and go long bond volatility. This seem to represent some sort of fundamental mispricing or complacency in the treasury bond option market, or unless I'm missing something here.