I did my Colombia trek with the Zulu 40 and it worked perfectly. The pack is made to stay off your back so sweat doesn’t stick to you, which is great in the jungle. I noticed however that the upper compartment on an airplane can easily fit a 65L pack, and not even long-ways, so why go for smaller? Yes, smaller looks neater, but it’s easy enough to tighten the straps and you have the extra room when you have to carry things for other people… so I upgraded. It’s not my go-to summer pack, but I haven’t used it much yet because I broke my leg and well, Covid.