Clark, one of the reasons the 75 meter DBZ is not as broadbanded is because you used RG-11 75 ohm coax to make it. 75 and 160 meters are very picky with that kind of thing. And if you used the RG-11 for the 40M DBZ, I am a little surprised that your SWR is that good, but then again 40 meters is not as picky.
Bazookas work best with regular basic RG-8 or RG-8X. Bazookas love leaky coax. Coax with tight shields do not perform as well, And never use a coax with a foil lining around the foam insulator to make a Bazooka. They still work but they are nowhere near as broadbanded.
It sounds like the 40M DBZ is going to work out very well. Mainly you will notice weaker signals seem a bit cleaner because of the lower noise floor as your video shows clearly. I watched your meter closely as you switched between antennas, and I think I saw a slightly higher signal on the Bazooka. Not a big difference mind you, but that lower noise floor alone makes it worth it. The choice of LMR-400 for feedline is a good idea. That is the only coax I use these days.
Good goin' Clark.