Hate to say it, but it really doesn't matter.
The only way I know how to evaluate is to compare the reaction of the respective solid/pearl versions of a given ball. I have the following solid/pearl combos of balls, with each combination having similar drills:
1) Motiv Ascent and Pearl Ascent
2) Ebonite Pivot and Pivot Point
3) Columbia Severe Delirium and Delirium
Over time, I've done fresh pad 500/1000 surface preps for each combination, concurrently. None of the Pearls react like the Solids with the same cover prep. Without exception, the pearls are a bit more anemic to oil.
If I'm missing something with the "it really doesn't matter", please explain.