I, for one, will not berate the S-lux 35 pre-asph. I have one and I like it. So, it might not have the sharpness of the Asph 1.4, but it doesn not have the flare problem either. Mine is usually on a M2 as a low light lens. I haven't come as far as a friend in Paris though. He uses the 35f2 IV generation during the day and at 6 pm he changes to the pre-asph S-lux! He is a Magnum member since the early 70's and knows his bl/w and his 35's.
It is small and compact, it handles well and its only real competition is the Nokton 40/1,4, but that lens is bigger.
The combination of a 35/1,4, a 21/3,4 and the S-cron or S-lux and a M2 will do very well, even compared to the newest glass. Particularly if you are a bl/w shooter. The contrast is manageble and you can do 16x20" prints without problems.
The filter size is bit of a hassle, but as I rarely use them, it is not critical.