Oh wow...I didn't know master rank existed, since it wasn't listed on Serebii. I thought that 7th star was for some kind of downloadable test GF would make or something.
Anyway, the first time I went through I got 5911 using my VGC11 team:
- Carracosta (Sturdy + Shell Smash + Mental Herb = win)
That's the highest score to date, didn't realize I was so close to "master". I now have something to do this weekend.
From experience, I know that length of the battle has not much of an effect on score. I remember that they kept sending Forretress against me, and with a team full of physical attackers, it took forever for me to kill. Every one of them kept spamming Iron Defense; it's like the computer isn't even trying to win, they just want to piss you off.