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Dave, all else being equal the TV Plossl should have very slightly better axial contrast than you will see in Nagler of the same focal length. I don't know if the difference will be large enough to notice though. This is simply a function of the number of air-glass transitions. There may also be a secondary effect of light scatter in your eye. The wider the field of view, the more light you will get entering your eye, it obviously follows that there will be a slight reduction in overall contrast. If this is to any meaningful extent, I could not say.
Where the Nagler hoses the Plossl is in it's field correction, the faster the primary objective, the more noticeable this will be.
I think it is also worth drawing the distinction between the metric by which we evaluate an eyepiece and the observing experience itself. Point being, I personally am prepared to accept the faults inherent in the Naglers and Ethos designs because perceptually, I find the interference of a field stop a greater offence to my sense of reality immersion than the 2% (or whatever) loss in contrast that comes with the territory.
This is a personal choice. ymmv.
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