I tried a stack extension on my Brazos. Added 2 foot of height. It did pull more air into the smoker. But the heat/air could not exit fast enough and heat would build on the stack end of the cook chamber.
The stack on the Brazos is 6" diameter. But the actual port between the cook chamber and the stack is 4.5". Some people have enlarged the port. I figured Old Country had a reason for that and I suspected it was to provide good support for the stack weld. I left it alone.
I had TelTru's on both ends. By adjusting the damper on the firebox, I could get heat balanced on both ends. The extension was easy to take on and off. I would put the stack extension on and the stack end would heat up. Take it off and it regained balance. If it had a collector/stack, the air could exit as fast as it entered.
So my final conclusion ....... the reason for the stack extension is to increase the draw through the smoker, but if I have to cut the air flow down at the firebox to keep heat from building on the stack end, then I've gained nothing.
The baffle is fairly large. It does restrict air flow. It creates a very small exchange between firebox and cook chamber. I concluded it created a venturi effect, air would speed up as it went under the baffle. Then opening up the air intake to the firebox, would cause the heat to shoot further into the cook chamber. That's why the air intake had to be cut down.
Early on with the smoker, I tried opening up the air intake and I got burned bottoms on meats on the stack end of the cooking grate. Even though my cook temps were not over 300*.
What the baffle does do is protect meats on the firebox end of the cooking grate, from direct heat from the fire. So it makes that end usable. Cutting out the baffle is going to make about 1/3 of the firebox end of the grate , unusable.
Air flow is about convection. Kitchen convection ovens cook faster than conventional ovens because they move air around the meats or whatever is cooking. There's no doubt that convection is a good thing. But how much convection is another issue.