veteran option traders like Tom Sonsoff say that in a study of 5 years data, selling straddles or doing iron butterflies have more profit, if the implied volatility is higher, ~=>50. since we are in a low vix period, is it less suitable time to do iron butterflies or short straddles now? high implied volatility = high vix? and low implied volatility = low vix, or have they nothing to do with each other?