However we know that there are cheap VI improvers and top shelf ones which are less prone to breakdown. In this case I would say you get what you pay for.
I'm no expert, but with different VII's you can often get caught between a rock and a hard place. Some VII are more efficient (bigger VI change for less polymer load), but these tend to be more shear prone. While the more shear stable VII tend be be less efficient and so require a heavier dose for the same effect.
More polymers that are more stable or less polymers that are less stable ?
If the polymer VII load is a contributor to deposits, the question could be phrased more shear stability or less deposit formation ?