I... can't.... Half of me recoils in horror at the impracticality, but the other half of me has a good enough armchair sense for the practicality of a high fuel

I... can't.... Half of me recoils in horror at the impracticality, but the other half of me has a good enough armchair sense for the practicality of a high fuel ratio antimatter rocket, so I can't say you're wrong :P