I have had VS10 for a couple of days now I have used VS since version 8. When creating a DVD from a 1.4GB MPEG2 (DVD Ready) file and setting everything to the same as the input file VS10 me the project will not fit on a 4.7DVD disc

The only way to make them fit is to lower the bitrate.
I know these files don't need rerendering and the bitrate of 9800v is OK as Nero 7 can create the DVD and the file size stays 1.4GB
What is going on? Am I missing something silly?