You need to model these spreads and try to quantify this "drift" you speak of. I still dont know exactly what you are referring to as drift, could mean lots of things.
What I mean is when two futures do not converge. This happens allot with index futures. What are ways to measure this before it happens? My bad for stupid questions.....
bump Have you finally figured out that ES vs YM at 1:1 is not neutral? Or as you call it "perfect" ? otherwise, Is the Dow still drifting?