Every so often, I visit either TDP or lensrentals.com and open up a browser tab for each lens I'd like to buy. Thankfully, my computer doesn't run out of memory during these exercises...anyhow. I then sort them in the order I imagine I'd buy them. (Keep in mind that a v1 24-70/2.8 lives in my bag, and a 24-105 lives in my wife's bag.) Honestly, I never reach for the 24-105, and I never find myself considering the 24-70/4. Instead, it's a battle over the order of the Canon 14/2.8, 35/1.4, 135/2, 300/4, and the Zeiss 15/2.8, 21/2.8, 35/1.4, 50/2/Makro, 100/2/Makro, and 135/2 (we recently added the 85/1.2 and 100/2.8L/Macro).