I know there is no correct or absolute answer to this question, but these threads have helped me sort through ideas, brainstorm with others, and overall make better decisions in the past. I'm strongly considering *gasp* letting go of my 135L in lieu of purchasing the 16-35 f/4. I find that while the 135 is arguably my best lens, it gets the least use. I'm not exactly sure why that is, but between the more versatile 85mm and the extra reach of the 70-200, it tends to stay in the bag unless I'm specifically shooting an outdoor portrait.
Would you sell the 135 (or any other lens currently in my kit) and pick up an UWA zoom? Let's hear your thoughts/advice...