I am trying to discover the name of a book recommended to me by my school physics teacher some 48 years ago. The premise of the book is that the proponents visit a world where the speed of light is comparable to the speed of sound and how this affects all aspects of life.
This is Mr. Tompkins in Wonderland (1939). After attending a lecture on relativity the protagonist dreams that he enters a fantastical world where light moves at a mere fraction of the speed of sound.
When he opened his eyes again, he found himself sitting not on a lecture room bench but on one of the benches installed by the city for the convenience of passengers waiting for a bus. It was a beautiful old city with medieval college buildings lining the street. He suspected that he must be dreaming but to his surprise there was nothing unusual happening around him; even a policeman standing on the opposite corner looked as policemen usually do. The hands of the big clock on the tower down the street were pointing to five o’clock and the streets were nearly empty. A single cyclist was coming slowly down the street and, as he approached, Mr Tompkins’s eyes opened wide with astonishment. For the bicycle and the young man on it were unbelievably shortened in the direction of the motion, as if seen through a cylindrical lens. The clock on the tower struck five, and the cyclist, evidently in a hurry, stepped harder on the pedals. Mr Tompkins did not notice that he gained much in speed, but, as the result of his effort, he shortened still more and went down the street looking exactly like a picture cut out of cardboard.
This could be Redshift Rendezvous by John E. Stith. When the titular starship Redshift is in hyperspace, the artificial black hole at its core, combined with the reduction of lightspeed in hyperspace, means the speed of sound is a quick run, while the speed of light is only several times that figure. Time dilation effects can vary noticeably between your head and your feet, you must wear a lifebelt to keep your nerve impulses fast enough to sustain life, and your watch will never agree with any other clock until you reset it after leaving hyperspace.
And in this bizarre environment, someone or something is killing people...
While this is clearly not the answer you're looking for, the Discworld novels by Terry Pratchett would fit the bill (if not for the recommendation being 48 years ago). In the Discworld, the speed of light is explicitly described (by the author) as being about the speed of sound, and perhaps less - my memory has dropped that particular detail.
Additionally, the speed of Dark is even greater, since that's how dark gets out of the way.