2-5 hits are needed I'd say.
Whitebeard dropped akainu with 2 hits, and if he didn't have super cancer, didn't get backstabbed by his strongest allied captain, didn't have a heart attack, akainu didn't get a free lava pumping into his chest when he couldn't react, 8 vice admirals didn't gank him, etc, he'd have done so without being hit himself. Every single yonkou currently is stronger than the whitebeard who was going into marineford more or less, his super cancer had progressed tremendously.
His striking power would probably stay the same, so the other yonkou would need 2-5 hits (though you could argue that his haki was wack asf, and he never pulled out the advanced haoshoku shit he did against roger), but ultimately the yonkou would win low or mid diff without really suffering any damage to themselves. (maybe blackbeard excluded)
Current Blackbeard's quakes would probably do more damage than whitebeard's quakes tbh.
You could argue that whitebeard > the others by merit of doflamingo's claim that whitebeard was the uncrowned king, but whitebeard was running on fumes going into marineford, any of the other yonkou would have crushed a post heart attack whitebeard with minimal effort.
But we literally saw akainu drop after 2 hits, and marineford akainu >>>>>>>>>> ishoo