I think the ad-detective defaults may have changed a little in version 6. You can set those to match version 5 if you like those better. I am unable to reproduce the "slower" results you first reported, and your own tests seem to rule those out.
Impressions are what they are.
I have tested V5 against V6, and I am unable to duplicate your results across the board, although I have seen some differences with individual sources. With others, QSF is quite a bit faster in V6. There are a lot of good things going on under the hood that weren't present in V5.
Yes, they've pulled some tricks to get "acceptable" results at suboptimal bitrates. I ran ffprobe and got one I-frame followed by 899 P-frames and 0 B-frames. 780 Kbps, which is low even for talking heads.
Good Catch! There are a few things "odd" about these Zoom files, including single-channel audio and 11 Ref frames, despite substandard video bitrate. Maybe a preset to make them "normal" mp4 (whatever that is)? I'll run some tests; I've got extra time on my hands and a handful of Zoom recordings.
Regarding your original question, Max Bitrate can be constrained more closely by setting vbv-maxrate and vbv-bufsize to the same value in an x264 command line, for instance:
--vbv-maxrate 10000 --vbv-bufsize 10000
I'm pretty sure these won't work in NVENC, since most presets are predetermined.
I suspect the reason you are seeing these limitations is because your BluRay burner or Virtual Drive is not being correctly recognized by DVDA: or, you are not in the correct menu, which can be easy to miss. I can assure you categorically, no such limitations exist within the program itself...
1. DVD Architect has no such maximum bitrate limitation. Since the average BluRay bitrate is around 25Mbps, I'm wondering where you got that impresssion?
2. DVD Architect will always re-encode your non-Vegas files, so you are degrading quality and losing a lot of time by doing so.
3. Vegas has...