Bukowski has a remarkably calm voice, I suppose that's how you get when you get old.
Or that's how you get after you survive the hell of his father. Or nearly dying alone and a feww other tortures he lived through. After some of that nothing else should excite you too much.
It would be interesting to hear a tape of him talking or reading pre-1954. If we believe that the county hospital incident was a near-death experience, then it's possible that he changed - slowed down - after he recovered. He has said that it was after that experience that he began writing more poetry, so something
changed in him.
Near-death experiences and head injuries have been known to make profound changes in a person's personality (near-death experiences that deprive the brain of blood/oxygen can have an effect similar to head injuries, apparently). There are a surprising number of comedians who suffered head injuries and whose families say they were different people after their accidents; Rosanne Barr and Sam Kinison are two that come to mind. But there are several others.
Hard to say in Bukowski's case, since I don't think anyone here knew him the late 40's/early 50's. ;) But I wonder about that sometimes. If Bukowski in his late 20's was the same slow, deliberate, slit eyed guy who eventually gained notoriety.