I thought you might see that and respond., since I know you have that new mower and have posted pics of it doin' its thing (and well I thought).
Maybe I'm still not be making myself clear though. I know what a tunnel deck was designed to do, and what they will do. I have used more of them than a true, deep commercial deck by far. They will flat out get it done, no question. I have a 60" commercial grade deck on my Deere CUT that is a tunnel deck, and then I have my 7 Iron. For most normal mowing there is no advantage one way or the other, but for high speed
mowing, and especially if it is moist, long and lush grass, the deeper commercial decks that are 5.5" deep over the entire deck area will handle and process the volume of material quicker and with less required HP. IME, the tunnel deck will start to leave some clumps if the grass is wet and thick, but the 7 Iron won't. The biggest thing that the MF diesel Z's need is more BTS IMO.