Hi Don,
Your source is “known” so that’s good.
You need to define your target(s) as a next step. There may certainly be more than one answer but here’s some of the questions:
Desktop presentation, what computer power and how projected.
Web presentation, connections speed and decoding power of typical targeted viewer.
Will it be a 40 continuous piece on a streaming (mms type) server or will you break it into multiple parts for progressive download (http type).
What is purpose of the video – business to business or high end target, consumer with less expensive slower broadband, public service or in regions with heavy dial up or slow broadband access.
One you define your target test and time the encode at the given target settings for a 2 minute section and you’ll have a good idea what 40 minutes will take, give or take.