What about one pocket with the side pockets, how much quicker/slower would the game be at the pro level?
I think it would be too different of a game. The side pocket presents a serious scratching threat in almost every game of one pocket. The head ball in the standard break typically ends up quite near it. Removing that threat, as well as the corner hooking opportunities it presents would change the game pretty drastically.
As far as speed, I suppose it might speed it up a bit, but I wouldn't expect too much, because removing those pockets isn't going to have any effect on the safety play and uptable moves that contribute to a game running long.
In terms of speeding up the game, there are some rule variants that require a ball to be spotted once a certain number are in the kitchen, to prevent uptable slogs. (AKA the Mathews Rule)