I have a lot of speedometer bounce after the first hour of over 60 mph riding..consistently. At lower speeds it's fine. I'm not altogether sure the calibration is accurate either..I haven't double checked with my Garmin yet, but I wouldn't be surprised if it was 6 mph off..
I'm not crazy about the oil or grease lubing of the cable, I think it adds drag, especially if you use grease. I have said that it seem that graphite would be the lube of choice.