We are off soon for a week on a small boat around the Galapagos and then a few days at a lodge in the Amazon and then some day tours. The 100-400mm II on the 5DSR is a must, but will be used by my wife. I'll take the RX10IV for general use and a TG5 for any wet outings. But, will I find the 400mm II on the 5DIV important or should I take my other 100-400mm II? The bare prime can do longer shots slightly better, and more so with the TC. It also has an extra stop if it is dim light. But, it is heavier and bulkier, and zoom is sometime essential. Any advice would be welcome.