I hate hunting in the heat; I hate heat in general. Too much Pennsylvania blood in me.
That said, the one thing that shuts it down for me is numb hands. If I had a way to keep my hands from going numb, it would pretty much never be too cold for me to detect. It's easy to keep your core warm (at least, it is for me) when you are moving AT ALL, and certainly there's enough "moving" when detecting to stay warm, with the right clothing. It's just my HANDS that are the problem...
Hunting (deer/small game, etc.) is pretty much the same, though I find it easier to keep my hands warm when I'm game hunting. Climbing up hills, or over obstacles, is enough to keep even my hands warm in most cases. Only stand hunting for deer is a problem for my hands.
Bottom line, I can hunt game in much colder weather than I can detect in, and it's all because of the "cold hands" issue. I have never found a pair of gloves or mittens that work, if you are not generating body heat through activity...
Steve