Update! I’ve added some reader comments, and my responses to them.
Just published in my Guide to Zeiss ZF.2 / ZE Lenses is a new holistic comparison between the $1732 Zeiss 21mm f/28 Distagon on the 24MP D3x, and the $6495 Leica 21mm f/1.4 Summilux-M ASPH on the 18MP Leica M9.
Both of these camera systems are very high performers, and I’m sure the comparison will be of interest to both Nikon and Leica users (and Canon users too). Is the Leica 21mm f/1.4 3.5X as good? Life is never that simple.