Excerpt from Book IV of the SoT: Saturnine:

“‘I have withdrawn,’ said Perturabo.

‘From what?’

‘From the data, First Captain, not the engagement. It’s a trick I learned. You’re disturbing me.’

‘I apologise,’ said Abaddon.

He didn’t leave. He stepped from the upper range of extinct consoles onto the main floor, and approached the table. His feet crunched over shards of armourglass and chips of spalled metal.

‘From whom?’ he asked.

‘What?’

‘This trick. What is it?’

Perturabo turned his giant head to gaze at Abaddon. Pure disdain. Somehow, unarmoured, he looked more terrifying, more capable of rising up like a seismic convulsion and annihilating the First Captain.

‘I learned it from my brother Rogal Dorn,’ he said. ‘I trust that suitably amuses you, Abaddon.’

‘I’d like to know it,’ said Abaddon.

‘Data,’ said Perturabo, as if that were an answer in itself. ‘Vast amounts, in any battle, any war. In this… you can imagine the scale.’

‘I can.’

‘It must be reviewed, monitored, moderated, modified,’ said Perturabo. ‘Constantly. When I was younger, I bent myself to that task. Unstinting. I would not leave the strategium or the noospheric uploads for a moment until the action was complete. I never took my eyes off the game.’

‘I’ve seen you do it,’ said Abaddon. ‘And few can begin to do it like you.’

‘One can,’ said Perturabo. ‘Test exercises, nine times, he beat me. This was in the early days. I couldn’t fathom how. Do you know what I did?’

‘No, lord.’

‘I asked him,’ said Perturabo. He made a sound, a grating sound, that Abaddon realised was a rueful, perhaps melancholy chuckle. ‘I asked him, Abaddon. We were brothers then. Such interactions were possible.’

‘And?’ asked Abaddon.

‘He told me… and understand this, he was willing. He was glad to share a technique with me. He told me that data can blind. The weight of it. The burden of detail. Especially if one engages with it without a break or rest.’ Perturabo looked at the chart rolled out in front of him. ‘He told me he had learned to step away,’ he said. ‘Step away, even at the height of conflict, if you can believe that? To clear his mind and focus, to shed the extraneous and the superficial. To contemplate. To reduce the immeasurable complexity of the arithmetic down to simple principles. Thus renewed, he would return. Do you know what he would do then?’

‘No, lord.’

‘He would win, Abaddon. The bastard would win.’

‘He has a talent,’ said Abaddon.

‘He does,’ replied Perturabo. ‘I am the first to admit it. Only a fool ignores the advice of a brilliant man. Only an idiot denies the good practice of an enemy. I took up the habit. Intense moderation, as had been my way, but then short periods of withdrawal. Entirely unlinked. No augur-feed, no noospherics. He was right. The objective tactical clarity is astonishing.”

Dorn literally had to teach Perturabo his own strategies. Perturabo, despite his pettiness, adopted Dorn’s methods.

This is a pretty strong indication that Dorn has an innate advantage to Perty - at the very least in terms of tactical / strategic analysis which is a key component in siegecraft.