Michael,
I think what you're looking for is the 12.5mm Zeiss/Docter. In your f/6.78 Dob it will give a 1.8mm exit pupil, just about the most frequently used range for most observers. It has high contrast, is tack sharp on-axis, and has a 90 degree AFOV. It beats the 12mm Nagler IV in every category. It has a noticeably wider true field of view, it's lighter, smaller, and doesn't blackout or kidneybean. The only things that keep it from being absolutely perfect are eyerelief (about 10mm) and a bit of softness at the edge, but with a 90 degree view you normally never notice. It's the most used eyepiece in my f/6 Dob.

Doug Tanaka