I was really confused by my single segment run being quicker on mission 1 than the previous best individual level time. So I decided to go back and try going nuts to see what what time I could get Mission 1 down to and here we are!

All I really did is do a brief pause at the first Ork base with a single squad of Marines to get the Waagh banner down early. That and being much more forward with the Leman Russ tank at the end.