For duration the 500mm mikado blades may not be the best. Use the stock woodies or 530-550mm semi blades.
The 600-15 on 12 cells will yield around a 1350 HS when run at 85%. It is plenty stable at that HS.
For that flying to the 85s are just right. Having only 2 lugs affects nothing as the force is along the body of the servo, not sideways.
I have mine setup with all JR 368's which fit everything just right. Add the Du Bro #675 arms and you are set!!