Gasser head question.
If you drop your tail blade length from stock to 95mm, you can run 700mm blades with no problems. The Gamma 700mm blades that MA brings in are a good value. They can be had from the various dealers for well under $100 a set. For a bit more money, you can choose the MAH 690's. SAB and TG make excellent blades in the 680-700mm range, too. If you will be a bit more specific about your intended flying style, I can suggest particular airfoil types. It all depends on how much inverted work you wish to do.
Ben Minor