Patty;
I don't know if this will help you or not but I will give you my experience during both periods.
I first went to DisneyWorld in July of 1995. I was there for 3 days. The temperatures were in the upper 90s to lower 100s. It was unbearably hot. I must also point out that I worked in Northern Greenland (about 700 miles north of the Artic Circle) at the time where there is a permanent icecap. Normal temperatures in Florida for that time of year would have been hot given the temperatures that I was use to. It was crowded, taking almost 2 hours to get on a ride. I felt that I was in one giant shopping center with a few rides thrown in to break up the shopping. This was suppose to be fun! How could anyone enjoy this. I swore that I would never go back.
Well, the friend who convinced me to try Disney suggested another time. Since about 1997/8, I have been going down to DisneyWorld about a week before Xmas. I have enjoyed Disney at that time frame and would recommend it to anyone. The shops didn't seem so annoying at this point but they were no longer the refuge from the heat. I have since gone down in early and mid-May, which have also been enjoyable trips.
Last year, I had some vacation time so I went down the third week in August. The temperature was in the mid-eighties, the crowds were okay, and it was an enjoyable trip. I 've also learned which rides and shows that I want to see, so they are targeted. When needed, although rarely, I will use the FastPass. One thing that the August trip had was a quick downpour would occur at roughly 3:00 PM each day. It was so regular you could almost set a clock to it. It was usually over in 15 or 20 minutes.
While it is something that you can't control, the temperature may be a deciding factor on how much you enjoy the trip. There were less crowds during the August trip than I remembered during the July trip. The late August trip was much more enjoyable.