David - just have to add the appropriate counter weight on the other side of the centre gravity. My current scope setup for the other eyepieces performs great for the 31mm Nag above about 40 degrees (ie holds position). Below this the weight of the eyepiece sends the nose of the scope to the horizon.
The "superwides" (and I assume you are talking about the GSO variety) work fine in the dob and I managed to test the range way back when Striker had them (how many sales ago was that!!
) The edge performance drops off based more on the focal ratio rather than whether its a newt or not. My dob is 12.5" F6 and I think the longest focal length I would use would be about 40mm (ie 42mm Superwide). Longer focal length eyepieces will have exit pupils that are too large for average person to get full illumination of the field and the secondary shadow becomes an issue (especially in daylight)