Please check your numbers. You seem to be missing "0's" on your posting, making some numbers likely smaller than you intended.

Yes, your use of zeros seems inconsistent and makes it a little hard to interpret. But if you are setting the minimum to the same as the average (I am guessing that is what you did?), then you are preventing it from varying the bit rate as much, making it more like a constant bit rate (it still varies, just not as much). This would greatly increase the render speed, but results in a much larger output file. So as long as it still fits on the DVD, you are reducing the wear on your cpu quite a bit! I wonder if you made all 3 settings, say 6,000,000? Would that be almost as fast as CBR? But the output file would probable be even bigger.

When you select variable bitrate the values DVD-A shows are not absolute in that low doesn't drop to 192,000 assuming you select the default value, rather it won't drop below that point and I suspect it rarely gets there, based on a real time review of footage rendered using other software that caculates the bitrate used and displays it as a moving graphic representation. Ditto for the average rate. Mean, perhaps would have been a better choice of description. Point is when you set variable bitrate it is all over the map and can get 90% or more or above that value whatever it is set to or for that matter 90% or more below based on what's in the frame being rendered. Another reason to let the computer, compute, rather than trying to second guess it by fiddling with the preset numbers.

Just a guess, someone at SoFo maybe can confirm, I suspect when you tinker with the values, lets say change the average from 6,000,000 to 4,000,00 and leave the max at 8,000,00 the net result is half of your video will render between 4M and the low value whatever it is set to with the result being clearly half your video now will never get a bitrate greater than half the max which for sure will cause a hit on quality where before a much higher percentage (difference between 8M and 6M on a percentage basic) would have if you would have left the defaults.

Someone else would have to confirm since I don't mess with the defaults. I would think to keep as much quality as possible BOTH the average and max bitrate values would need to be changed so that a greater proportion of the vid is processed above the average rate as it would be in the defaults rather than making half the vid never have a chance to get above the average rate and thus benefit from high bitrates between the average value and the max whatever the values are changed to. Hope this makes sense.