"Medium to Heavy oil" is too large a range for any ball today to cover.
If I had to guess I have 2 of them with different drills and different surfaces), I'd say the WC, with an average drilling, can cover medium-heavy oil for the average ball speed person with average revs. If one had more ball speed than revs or vice versa, then it would a medium oil ball. If one had more revs than ball speed, it would probably cover into the heavy range.
Sanding the surface will allow it to handle more oil and polishing will make it handle less.
--------------------
"None are so blind as those who will not see."