Hey
@maven48
As a fellow Vegas user, I know your pain! When I was working on my Phase IV edit I was never really happy with the MP4 rendering... however, even when I used Handbrake it really wasn't much better. Anyway, after a lot of research and seeing what other people do by watching various youtube tutorials or guides, I settled on the following...
Format: MAGIX AVC/AAC. MP4
Variable Bit Rate
Maximum Bps: 20,000,000
Average Bps: 12,000,000
Encode Mode: NV Encoder (or whatever your graphics card might be)
Preset: High Quality
RC Mode; VBR - High Quality
Audio: Sample Rate: 48,000
Bit rate: (bps) 384,000 or 448,000
These settings have worked well for me when I did my Moonraker Edit and for a 2 hour movie produced a file of 13GB in size. Now, granted this may be too high for some, so you could play around with the average bps and as you say, try 8,000,000. Personally I don't mind a big file as I want really good HD quality.