Do you know what the differences are between the
6.85 GiB - LinuxMCE Install/Upgrade DVD for i386 - 0710 Beta 4
3.71 GiB - LinuxMCE Install DVD for i386 - 0710 Beta 4?
If I understand other comments correctly, we can upgrade with the 3.7 GB version and the upgrade script, so what's in the other 3 GB?
No, I don't know this exactly - but looks like 6.85GiB image is a double-later DVD with both i386 and amd64 arch binaries there. Useful for mixed configurations probably (e.g. i386 core and amd64 M/D). Mine one was i386, so I just used 3.71GiB beta4 DVD for the upgrade.