First here is my trendline chart of the SPX. You will notice the line from the bottom to the first major dip. And the recent price action could almost be seen as a "backtest"

Now for the SPY chart. You can see that it recently already cleared the backtest. Which is an interesting bullish difference. On the other hand, an interesting bearish difference is that the money flow (as measured by the CMF) is much more negative for the SPY as compared to the SPX.

There is nothing definitive to be gleaned from comparing and contrasting these charts yet. But I wonder if we will find some more divergences when we get closer to the top.