Paul, you would definitely get a bigger field from a larger 2" eyepiece. It might not fill a stop-less eyepiece like my TMB40 to the edge, but it's well worth trying to see which eyepiece it can fill.
Kidney-bean and blackouts (commonly seen in some Naglers) is a result of spherical aberration at the exit pupil of the eyepiece; some particular Naglers were particularly well-known for this. There are other UWA eyepieces that don't suffer from it so badly.
The true field of view is determined by the diameter of the field stop at the bottom of the eyepiece. If you lay all your eyepieces on their side, and look into the barrels the one with the biggest hole has the largest TFOV. See the photo at top centre here
http://web.me.com/wx88/Site/Optical.html
The technically-minded can reach for their calipers and measure, to be sure of this.