I wouldn't call 40°F 'warm'. And between 40-50°F I find it's best to try and keep rain water off my hands (and the rest of my body). There's a gray area between 50-57ish°F where I can go either way depending on how hard I'm working. However, my hands sweat a LOT less than the rest of me so I'm pretty tolerant of being over-gloved. Too much on my core and I'm a disaster, though.