You can fit 2h 50 minutes of 1080p video on a single layer disc at 17 mbps VBR. Using H.264 compression, this should still look good... especially if you are using the new
x264 Pro encoding plugin that produces fantastic studio quality results even at the lower bitrates. It uses x264 at it's core, so the quality is MUCH better than the default MainConcept encoder that is built into the Adobe Media Encoder.
Good luck.
Jon Geddes
http://www.precomposed.com