I don't know about the 28/2. Too much money for a lens for me - I would
be afraid to use it.
I do use the 35/2 Summicron v3 (got mine like new in the box for US 700).
I like it for its compactness and close focus, mostly - its very small.
And I believe you get more lens for the money with the
v3, since the v4 has achieved such a cult status. Also, the 35/2 v3
has only 6 elements which I personally believe makes it more flare resistant.
At f2 it does behave similarly than the 40/2 CLE M-Rokkor and the
CV 40/1.4. Here you can see what I mean by flare resistance:
BTW, the Canon 35/2 and the UC Hexanon 35/2 (available on ebay
new for US 899) behave very similarly, since they share the basic design.
I should have asked before: what 50mm do you use ?
The 35/2 works very well together with a contrasty sharp 50 (I use
it in the same kit as a Canon 50/1.4 - similar behavior to the Nokton 50/1.5).
If you use either Canon 50/1.4 or 1.8 it is a great match.
Best,
Roland.