Are there differences in orthodontic/orthopedic outcome that can be expected using mara appliance & braces vs. braces & elastics to correct an overjet?

Yes: yes there is a huge difference in how and why you would approach both as an option for treating an overjet. A lot of time you will do both in a case but I would confer with your orthodontist or make an appointment to gain more knowledge about your concerns/question.

Gold standard: Gold standard is braces. More important than the hardware, however, is the operating system.. A fully qualified Orthodontic Specialist would know, for example, that you can't do Orthopedic Treatment on a non-growing individual. Please don't try to self-diagnose and treatment plan. See an expert, an Orthodontic Specialist, who will be able to properly guide you.