I have sonnar on rollei 35s and indeed they are very different. I bought the rollei after fall in love with low price and saturated colors.
But I think Summitar is like an old painting , I agree with smoothness and low profile colors but its degrades , so long degrades and relief effect and night performance is not with sonnar. If you took intense colors film , a slide film and sonnar is so good but not classical feeling , its like wall mural modern.
I love with Contax , Biogon.