I can answer a little, 30mm is 30mm whether it is a 1.25" or 2". A 30mm 1.25" plossl gives near to the maximum FOV that you can get from a 1.25" EP at maybe 42ºish but so does a TeleVue 24mm Panoptic with its 68º FOV. Moving to a 2" means that you may be able to get 80º FOV in a 30mm as opposed to the constrictive 42ºish.
Moving to 2" should give better off-axis views because you're using less of the usable FOV.
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