The two files are the same length. To be honest, I never thought about CBR vs VBR, I thought that while VBR varies, it averages out to a bitrate over the file, which in theory should be the same as a CBR of the same throughout.
It seems that Mediainfo is reporting a different bitrate than Windows and what Vegas renders out as according to the settings in Vegas. Windows reports the new file as 3500/160=3670 total (which is what I set in Vegas) but Mediainfo reports it as 4411kbps with an audio stream of 160kbps, Why would setting it at 3500 in Vegas produce an output file of 4411?
8557_vegassettingmismatch.jpg.zip
Pic attached is my settings and the resulting output file in Mediainfo.