Yes, the green speed can vary somewhat, particularly by course.
When you notice you're coming up short constantly, like 2 or more holes, you need to use 8.0 or more instead of 7.7 per 10 feet of scale.
I always find Merion a bit slow, and I have found being aggressive (8.35 to 9.1 per 10 feet of scale) when putting on Merion Tournament speed greens can save some strokes.