In other words, Even-faster-Rainbow-Dash-with-her-friends-Run.
This record itself is not so satisfying but I got too tired to improve any more.
Especially after discord stage 3 is messy but survival speedrun is just too hard (and discord stage is hard to practice too because save is not allowed in survival mode) x_x

In Survival Run, you can cancel all actions (including RD's sonic rainboom) by character change. This allows RD to spam sonic rainboom faster than Mane 6 Run.
Furthermore, character change resets flight state too. It means RD (and Fluttershy) can fly infinitely with proper input, and can fall at normal speed after flying.