I agree that the Guardian, with a few modifications, can be an excellent performer. I wrote the modifications I made up in detail in the July-August, 2009, issue of Hi-Low Landings and I recommend you look at that. The main mods were to remove the outer bay on each wing, to reduce the height of the fuse by trimming up to 3/8" off top and bottom, and putting the controls external, below the wing. I did not change the airfoil. Bill Calkins, the designer, would agree that removing one bay from each tip greatly improves the performance of the model, so at least that trivial modification is highly recommended.
I have had fatigue failures of the aluminum rod used to make the support of the line slider, so I recommend that anyone using a line slider change the mounting method to something more durable, perhaps steel wire or perhaps plywood struts.
I strongly recommend putting the bellcrank eternal, below the wing and keyed into the fuse with the ply fuse doublers extending all the way back past the bellcrank platform. The controls will be accessible for changes you might wish to make to the leadout system later. For example, you might start with fixed leadouts at the "normal" position, then gradually move them rearward to see how you like it. You can have fixed leadouts near the trailing edge and hang the model. If you like it, you could add a slider later, since everything would be external.
Pete