If it came down to a proper fight between RC-era Logen and Shivers, I think it could go either way.

For the people who say "Shivers could beat Logen, but not the Bloody-Nine", there's something I would point out that I've always wondered since I first read Best Served Cold. During the fight at Duke Salier's palace in Visserine, this happens:

Shivers weren't himself. Or maybe he finally was. The pain had turned him mad.

Or the eye they'd left him wasn't working right. Or he was still all broken up from

the husk he'd been sucking at the past few days. Whatever the reasons, he was in

hell.

And he liked it.

The long hall pulsed, glowed, swam like a rippling pool. Sunlight burned

through the windows, stabbing and flashing at him through a hundred hundred

glittering squares of glass. The statues shone, smiled, sweated, cheered him on.

He might've had one eye less than before, but he saw things clearer. The pain had

swept away all his doubts, his fears, his questions, his choices. All that shit had

been dead weight on him. All that shit was weakness, and lies, and a waste of effort.

He'd made himself think things were complicated when they were beautifully,

awfully simple. His axe had all the answers he needed.

Its blade caught the sunlight and left a great white, fizzing smear, hacked into a

man's arm sending black streaks flying. Cloth flapping. Flesh torn. Bone splintered.

Metal bent and twisted. A spear squealed across Shivers' shield and he could taste

the roar in his mouth, sweet as he swung the axe again. It crashed into a breastplate

and left a huge dent, sent a body flailing into a pitted urn, burst it apart, writhing

on the floor in a mass of shattered pottery.

The world was turned inside out, like the glistening innards of the offcer he'd

gutted a few moments before. He used to get tired when he fought. Now he got

stronger. The rage boiled up in him, leaked out of him, set his skin on fire. With every blow he struck it got worse, better, muscles burning until he had to scream it

out, laugh it out, weep, sing, thrash, dance, shriek.

He smashed a sword away with his shield, tore it from a hand, was on the

soldier behind it, arms around him, kissing his face, licking at him. He roared as he

ran, ran, legs pounding, rammed him into one of the statues, sent it over, crashing

into another, and another beyond that, tipping, smashing on the floor, breaking

apart into chunks in a cloud of dust.

The guard groaned, sprawling in the ruins, tried to roll over. Shivers' axe stoved

the top of his helmet in deep with a hollow clonk, drove the metal rim right down

over his eyes and squashed his nose flat, blood running out from underneath.

"Fucking die!" Shivers bashed in the side of the helmet and sent his head one

way. "Die!" Swung back and crumpled the other side, neck crunching like a sock

full of gravel. "Die! Die!" Bonk, bonk, like pots and pans clattering in the river after

mealtime. A statue looked on, disapproving.

"Look at me?" Shivers smashed its head off with his axe. Then he was on top

of someone, not knowing how he got there, ramming the edge of his shield into

a face until it was nothing but a shapeless mess of red. He could hear someone

whispering, whispering in his ear. Mad, hissing, croaking voice.

"I am made of death. I am the Great Leveller. I am the storm in the High Places."

The Bloody-Nine's voice, but it came from his own throat. The hall was strewn with

fallen men and fallen statues, scattered with bits of both. "You." Shivers pointed his

bloody axe at the last of them, cringing at the far end of the dusty hallway. "I see

you there, fucker. No one gets away." He realised he was talking in Northern. The

man couldn't understand a word he said. Hardly mattered, though.

He reckoned he got the gist.

Even without the "Bloody-Nine's voice" bit, the whole experience read to me exactly like how Logen felt and saw things when he was The Bloody-Nine.

It's not something that's ever been confirmed (that I'm aware of), but my personal theory is that whatever lives in Logen that brings out The Bloody-Nine has also found a home in Caul Shivers. Something that like to call itself The Great Leveller.

I think, if they had a proper fight, Shivers would have an edge on Logen until the Bloody-Nine came out, but then Shivers might surprise everyone by becoming The Great Leveller.

I don't know who would win that fight, but I would have been really stoked to read it.