>If you back test over the past 20 years then I'm not sure it helps much as the market of 20 years ago didn't really have any of the major market drives of today's markets, HFT's, huge numbers of hedge funds and the money they bring, and huge passive investing via ETF's, all those factors were there 20 years ago, but they weren't the major market drivers that they are now.

well, giving the fractal nature of price movement, i'd guess one can backtest against last several days/weeks taken at very high resolution and scaled out to represent months/years :)