The reason the prefs have upside beyond par is the possibility of a conversion. I place a high probability on it, given that we have heard Calabria (in a TV interview), Mnuchin (in Treasury's plan), and Phillips (in two separate talks) talk about it.
There's also my thesis that the commons' greatest reasonable upside is still less of a gain from here than the prefs, even without a conversion. Given how heavily weighted towards the prefs the big-money investors are I think they, in aggregate, agree.