Lee,
I would not use any GS other than the 7/8 (and even this line will overload the rod) on the Sage 9140 (I assume you have the 9140-4). It is such a soft and slow rod that will be greatly overloaded with even the 8/9 GS, and the 9/10 GS would probably blow up the rod. I own a 9140-4 and I won't let a GS or XLT get near it. The rod was designed to cast short lines (Skagit style, Scandanavian heads, Windcutter) and not the long-belly ones. Be very careful using a GS on this rod to avoid blowing it up.
That said, the basic approach with the long lines is the same as with the short- and mid-belly ones. You need to move more line, add more power to all your casting moves, use a longer stroke to keep the extra line aerialized, and start your forward, final delivery a little before the D Loop has finished forming. Dana has some video showing this forward delivery starting before the D Loop has finished forming on the forum.