They throttle/they don't throttle, shared resources are saturated/not saturated, we can argue 'till the cows come home but arguing doesn't resolve the problem.
@kayfour has already reported varying speeds, the only question is what causes them.
Presumably any throttling or saturation of shared resources (if present) will be most evident during peak times and to that end maybe regular speed tests seven days a week both within and without these times will yield some useful information.
