I'd guess that compared to Primebeard, the old one in Marineford would be at ~30% of his former power. Like the commentor before me said, "Whitebeard in his prime was absurd" and to add to that "He was the one who fought neck on neck with Roger".
If he had whished to do so, even old Whitebeard could have sunk Marineford single handedly, but he didn't do that because Ace and his family would have been in harms way aswell.
XDArthas
2022-04-14 22:18:04 +0000 UTC
More like 650-700
Lor_D_Richafa
2022-04-13 09:20:56 +0000 UTC
Whitebeard in his prime was absurd. Only Roger and Garp/Sengoku could match him. Without saying anything there's a flashback in the current arc that shows off Whitebeard in his prime and it's absolutely glorious. Sadly, that's nearly a thousand episodes later from this.