Let's see the MD has day and night domestic and international.
The Bus has day and night domestic and SIBA.

The real difference seems to be with SIBA you are still doing multiple leg (night?) hub turns while on the MD, despite the multiple time zones, you stand a better chance of being able to have a little longer layover. Although it may be my imagination but many of the pairings seem to be becoming worse due to s-optimization.

And I agree, 60% is a good number if you want QOL.