Note the Tele Vue Everbrite diagonals are a one piece construction to ensure alignment and won't rotate with heavy accessories attached.
See
http://www.televue.com/engine/TV3b_p...d=62&Tab=_90EB
The Tele Vue 2" Everbrite will accommodate the 46mm field stop of the 41mm Panoptic so you will have no trouble with the 38.7mm FSD of the 35mm Panoptic or the 42mm FSD of the 31mm Nagler.
You may not notice vignetting with a smaller clear aperture but it will be there and if you are doing critical work like estimating variable star brightness then you need zero vignetting (and of course other aspects of the telescope design require you to have a 100% fully illuminated field for the eyepiece you intend on using). Vignetting is stronger closer to the field stop so if at the front of the 2" nosepiece of the diagonal you may not notice it but if at the bottom of where you inset the eyepiece it will be noticeable and this is where it is more likely to be in a poorly designed diagonal.