>>3798020f2.8 is nice
f4 is what you need
my favorite lenses i have ever used are the 21mm f4 and 35mm 2.5 skopars on 35mm.
on medium format i dont think ill ever have a system that shoots faster than 3.5 on the RBs. the 127 3.5 has as narrow a dof as i imagine i'll ever use for portraits