This is a weird question for me. As a DM the time I spend per round controlling creatures is basically always less then a minute, at most. Each PC gets their own color of die, I roll damage and to hit at the same time, and while I'm asking "does Y hit" I'm adding up the damage. The first time an ability is used I describe it, but otherwise it just doesn't take very long.
As a player my turn doesn't take more then 20 seconds at most (often under 10).
No one else in my group is that fast. If they were, combats would never grind. In my experience the grind is primarily a social issue (people not paying attention to when their turn is coming up, people going to the bathroom, people forgetting out of turn attacks because they weren't paying attention, people not knowing their modifiers, people dithering on power use, etc.). If you do any of those things as a player, or as a DM, and you experience grind? The grind is your fault.