I am just re-exploring my M9-setup (I do that every 1-2 years after coming back from other "journeys" like the K5 or the Nex).
And while I still own and keep some f1.4 M-lenses I now enjoy a lot the tiny 35 and 50 Summarits. It is not so much about carrying a little more or less weight, however its nice to pack it in an even smaller bag and I kind of like the handling and the "classic" and simple feel of those small lenses.
I am even tempted to replace my 21/2.8 with a 21/3.4.
There is a lot of talk about the 1.4 glass, but f2.5 on ff-sensor isnt exactly slow.
So I wondered if there are crazy guys like me who own several focal length in 2 versions (1 fast and 1 compact), and even more interested which is the best compromise for YOU between speed and portability.