I checked with a couple trenching attachment manufacturers, and yes, high flow yields much more torque and will do the same job significantly quicker.
Sometimes salesman are too focused on selling to the lowest price point. Meaning they dont want to suggest high flow because it adds another couple K to the price of a machine. Most having never been an owner or operator of an excavation business they cant sometimes see the value of spending more upfront to be more productive which makes more money throughout the ownership of the machine. They dont want to lose a sale to someone else that successfully talks you out of high flow and sells at a lower price point. So when you talk to some of these guys just keep in mind their prospective, the vast majority mean well they just dont have an in-depth understanding of this business in some cases.