That is my current thinking.

I feel that it is better to go 50mm f3.5 Elmar (for size) and 50mm f2.0 Summicron (speed/performance) or just compromise with a 50mm f2.0 Summitar or 50mm f2.8 Elmar. But the purpose of a collapsible is to be compact, the the Elmar might win, and it is easier to deal with filter-wise (39mm, i believe?)