I read this assessment about heat/humidity training a few years ago, and I think I mostly agree with it, and it goes like this:
Humidity/Heat training is most beneficial if you are going to be racing in heat/humidity. However, training in heat/humidity will NOT give you additional benefits over training in cooler conditions if your target race is going to be under cool/good conditions. If you think about it logically, if training in heat/humidity yields additional benefits over training under good conditions, you would see tons of elite athletes going out in the hottest part of the day to do their training instead of going in the early mornings or late afternoons when it's usually a little bit cooler. (The exception is when they are training for a target goal race that they know will most likely be in crappy conditions with SI index north of 150).
While it's true that training in crappy conditions and at elevation both slow you down, the biggest difference between the two is recovery. When I go out and run a workout at 6000+ ft altitude and cool conditions, I know I am going to be about 10-13s/mi slower than at sea level. If I were to do the same workout at sea level with a SI in the 140-150s, I know I'll also be about 10-15s/mi slow. However, I can recover from the first scenario much much quicker because my body won't be subjected to the heat and water loss of the 2nd scenario.
Unless you know there's a good chance your target race is going to be hot too, I would just try to move your quality sessions to the cooler parts of the day, assuming you have the room and flexibility in your schedule.