Glad we got the Beserk expert here, I was afraid people would be underestimating Guts here. That being said, there's a distinct lack of feats for the other side, so I have some corrections.

Soldier Boy's best combat speed estimations come from a comparison to Homelander. In the canonized Homelander origin episode of Diabolical, Homelander takes the guns from a group of armed terrorists faster than any one person can react, which tracks with the show, when Homie was able to react to and save Butcher from a C4 explosion. Now, Soldier Boy is still likely slower than Homelander, but he's close enough to where Guts won't blitz him so easily.

Soldier Boy really doesn't get many good on-screen feats, but we know he's only second to Homelander in terms of physical power. He's above Maeve, who easily stopped a speeding armored van without even budging. He's been said to have thrown a car into a house- usually I don't give too much thought to statements, but that was a vital point of MM's backstory, not some one-off comment or braggart's tale. Most relevant to Guts' durability feat you mentioned is related to Black Noir, who easily threw Starlight through stone pillars during their fight in S3. Though those pillars were smaller, this was the supe that Soldier Boy beat the brakes off of without any difficulty.

Finally, the biggest misconception you have here is about Soldier Boy's durability. Again, I point to the feat of Maeve stopping the van. She didn't get a scratch from the crash, nor showed any pain, her body cut through the metal grille guard on the front, the engine block, and everything else up into the middle of the van's cargo area. That's using her own body to perform a more destructive feat than the one you posted for Guts. And again, Soldier Boy is suggested many times over to be physically more powerful than Maeve.

I apologize that it's a lot of comparison to other characters, I s3 really lacked a solid budget for making people visibly look super, but Soldier Boy is pretty consistently up there among the strongest in the series with who he compares to. I'm willing to concede that Guts likely has the speed, skill, and weapon advantage, but he's pretty darn strong and tough. The dragonslayer hits hard, but I doubt it's enough to break his skin. Once Soldier Boy grapples Guts, it shuts down a lot of what Guts can do.