I just ran a test that may be useful.
I started with 4 random WMV files of about 20 minutes in length. I edited out about a little over half of each of these files. I then combined the stuff I wanted to save into a single WMV file of 32 minutes in length.
I did this with Movie Maker 2.6 (available as a download) and with Movie Maker 6, which I copied over to Windows 7 from an image of an earlier Vista installation. I just dragged the Movie Maker folder from C Program files of the Vista image to C program files of Windows 7. The only change I made to the Windows 7 install was to re-register a few DLL files as recommend by WiFi Ed of this forum.
Here are the results:
MM 2.6 results in a WMV file of 476 MB, which took 90 minutes to process on my PC.
MM 6 (the Vista application) results in a file of 345 MB and took only 18 minutes to process.
One of these files runs 32`10" and the other runs 32' 12". I tried to make them the same length and came close.
The only differences I immediately noted in the interfaces was that MM 6 permits frame by frame advances of 3/100 of a second, with very little lag. MM 2.6 frame by frame is 7/100 of a second and has considerable lag--you have to wait on it for the frame to change.
I can't tell any visual difference in the finished versions.
Here are the detail tabs for the properties of each file. The first one is for MM 2.6; the second one is for MM 6, the Vista application.
Make of this what you will. I am not sure what it means, but I'm going with the Vista application for the lower processing time.