Hello all. I just found this very interesting thread.
Bone has openned my eyes. I've done some statistics study with SPX/DOW daily price data since last night. If you plot daily close spread between SPX and DOW, it is a unbelievably amazing divergency indicator for SPX/DOW price movement (daily). This is much better than MACD/OBV/NY updown vol, or whatever you name it.
In terms of trading ES and YM, I did a brief study based on SPX/DOW inraday open/high/low/clsoe data and very limited future data. With a automated system and some statistically generated triggering threshold value, the spread pair trading can have extreme high winning percentage.
Onething is very interesting. If you trade ES/YM spread for intermediate term, you probably still need knowledge about market trend in order to profit on spread increase or dicrease. Anyway, if you know for sure what the trend is, you can trade anything. The beauty is, if you trade intraday only, you don't care what the trend is based on my statistics study at the moment. However, there are some small technicallity things you have to take care of, such as slippage, execution timing, etc.. There are just virtually infinite possibility to trade spread.
I did a ES/YM spread paper trade today and had a little more than 50 USD less 14 USD commission by market close(2 RTs 7 USD each RT in ThinkorSwim paper account). It was much less stressful than scalping.
I'll try to get some intraday 1 minute data for ES/YM and conduct some more rigorous study/backtesting.