I have a set of Alpinestars 365's which I tend to use most of the year unless it's extremely cold (<5deg C) or hot (>20deg C).
Really I just tend to go with looking out of the window and making a guess! I used to have some Gerbing heated gloved which were wonderful in the winter, because they were heated they didn't need to be so thick, and so toasty warm too! Now I use Held ones, can't remember which model, but they are also warm enough down to freezing on long rides. Much colder and it's heated grips time!
In the summer I have some Held perforated gloves which are joyful to ride in when it's really warm.