One thing not mentioned here is that there are two ways to design a VC paper. One can take advantage of being rather invariant to printing filter(s) particularly in the mid tones. But, another method of making a VC paper gives vastly different speeds at each contrast grade.

The first method is more difficult than the second and therefore, you will find that top grade papers are close to being invariant with a small filter factor, but papers from 3rd tier manufacturers may vary by several stops as contrast grade varies.

This will generally be the case with graded papers from the same companies.

The reason is that top grade companies will design an emulsion for each grade and tailor the speeds to match, but 3rd tier companies with less R&D money will opt to use 1 emulsion and force fit contrast allowing speed to wander all over. Generally, speed goes up with contrast in these cases.

So, result also depends on paper.