To me, 50/1.8G is really a good lens which should be better at closer ranges. My concern about any f1.4 or faster lenses is the potential cut-out of the bokeh circle caused by the mirror box. So, an f1.8 or 2.0 lenses would rather be more ideal to me.
You should try the Tamron 45/1.8. Compared to the 50/1.8G, and FL difference aside, it provides even better (uniform) sharpness wide open, lower vignetting, excellent coma correction, and as a bonus : VR and sealing. Maybe a tad less contrasty, not really Zeiss-ish. A good match for the 300/4 PF.
Apparently I must be the only user in this forum ?