Entirely untrue, the faster you mow, the more acres you cover given the same deck size. Pretty simple.
Taken out of context. That statement goes with the second part I said. More or less meaning just because you can go faster "with a smaller deck" dont mean you will get done quicker. The "IE:" after my statement says that. (IE means example...)
I think that is wishful thinking that you doubling your mower width automatically equals half the speed. Mower weight, pto hp, and vegetation density play a huge role in figuring this out even though in theory with an equation it works out.
Mower weight...maybe. PTO HP an vegetation density no. Thats where 1/2 the speed comes in.
Just because you go to a larger mower, doesnt mean the PTO HP changes. HP defines work/time. You try to do twice the work, and go half the speed.......SAME HP requirement.
LD, if you can mow faster you will get done quicker with the same size mower there is no arguing that unless you only take half swaths. There is a generic formula that mathematically calculates your acres per hour but that's not taking into account the size of the tractor or the density of the growth. If your only goal is to clip a pasture or take off two inches of grass than I think we are splitting hairs and I think you could run a larger mower. If you are actually brush hogging with 2' tall thick weeds, we are in a whole different ballpark and I stand by my argument that the 5hp/foot is a good rule of thumb and should be the minimum recommendation for the average user without special circumstances coming into play I.E terrain, trees, growth thickness. I think if you are well below the 5hp/ft rule of thumb for a mower, you are going to be lucky to go 1/3 as fast as with a cutter that is twice the optimum sized cutter. I really doubt that doubling the mower width is going to cut your speed in exactly half. I'm sitting at almost 7hp/ft of mower and I wish I had more when mowing tall fields at 4mph-4.5mph. Both the terrain and the pto power are limiting me to that speed.