The Green is now at low flow. 520 gr seems like a lot of weight that will go "splat!" when it's time to be fishing fine and far off. A 7 wt fly line and long tapered leader seems more appropriate to water conditions.
Not sure what 'Green River' you're asking about, but with 2-hander's folks have a great tendency to go far longer than needed. 'Normal flows' a 9' is fine, a 12 foot is more than needed. A Sink tip/Poly-sinking 2 -3 foot to fly. Beyond that you need a weighted fly. (Trust me on that one.)
Low water, like really low water ....., now the 12 -15 foot floaters bring something to the Party.