In response to Michael Arnowitt- None of my sources list the sonata. The National Library of Canada, Ottawa has G.G.'s manuscripts. I think that is where Carl Morey got the Klavierstucke.This is a recent publication Perhaps the G.G.Foundation or the Friends of G.G. will publish the sonata. I hope so.
I am interested in what speeds you are playing the 5 Short Pieces. On #1 I use rubato and play between eighth note = 96 to 112 depending on my mood. #2 I do around a quarter note = 60. #4 I play a quarter note =112. I am undecided on the rest.