MMM is right on. I would suggest at least a 7wt in a 9'6'-10' range. Great for mending/roll casting. On the OP, I would go minimum of a 7, I normally use an 8wt for summer (but am getting a Sage 7136 for my summerrun spey fishing though). You hook into those pig springers or big summerruns, you would really have to play them right to land on a 6wt.

Agree again with MMM. 30# backing is way to go. 20# is a bit light. I've seen these fish eat 20# leaders, wouldn't want something holding my backing to be that light as well. LOL.