TomChivers wrote:
However, as stated the rule has the apparently unintended consequence that if you beat someone >40 points higher than you, your grade is capped as if they were only 40 points higher than you
In the mark one version of the grading system back in the 1950s, no such rule existed. With the growth in weekend tournaments towards the end of the 1960s, mismatches became more commonplace and as you state, you would lose points by beating someone more than 50 points below you. Moving it to 40 points was a quick hack to the system which had the effect of removing the worst of the anomalies.
The anomalies are still there of course and put a brake on the grade change for anyone rapidly improving or rapidly declining. It also applies the other way. If you have a grade of 100, get paired and lose against a player of 180, then you score 90. If you have a grade of 130, your survival chances aren't much better, but you get a performance of 120.
That said, for the most active player, the ECF system has less inertia (memory of previous ratings) than Elo style systems.
The international Elo system used to cut off at 350, but it's now been moved to 400.