Fly rods can be quite effective at whipping large fish. One needs to flex the rod into the butt while keeping the tip straight. Any questions about the effectiveness of fighting big fish with a fly rod should read some about Andy Mills and his tarpon skills. (http://www.floridasportsman.com/flyfishing/0501108/)

To address the initial question, if you already have a 9 weight I would recommend a 7 weight.

Regards, Keith