On a hacker A 50 16L I found the 18x10 to be perfect. I never got to the point of trying Hezik's cut down 19 x10, as I felt the downline braking was fine as is.
I just did a bit of quick and dirty math, and your RPM on the 12L will be similar to an A50 16L on 6s. You might find that adding larger capacity packs you'll want that extra pulling power.
Incidentally, I tried 6s on my mythos, and I didn't like it, the amp haul from 6s is pretty heavy, and I found it didn't take much to overdraw my packs on a windy day. I upgraded the motor to an 8s setup, and now I have power and longevity, and my 6s packs are used occasionally on my 90's pattern planes to mimic a hot 60