I'd suggest you drill them the same. I used a strong pin on my Freeze and it's strong enough to handle true medium oil for me. I'm afraid to drill my Burst right now. The Burst is supposed to be for medium oil.
I think the Momentum cover on the Freeze is strong enough to handle more oil than expected for such a low price.
Oh, and both balls are already at 4000 grit + polish. So there's darned little you can do to make them weaker, surface-wise.(I used a white Trizact, cerium oxide, pad and 4 coats of Delayed Reaction. I didn't want to re-drill it.) Drilling is all you can do.
"None are so blind as those who will not see."