1st...Keep calling, you never know.
2nd....8:50 is not as bad as it sounds. We had a ressie at 9pm back in December. I wasn't sure it would work out, and right up until we got there, I was prepared to bag it. I forgot that we would be on "Disney Time" and that my son would still be running strong on the excitement of it all (we did have a nice snack around 5pm)... also, I was glad to get back to the room after dinner and just crash.
3rd....Do not worry about the crowds. We had the same problem with ressies back in December (which is why we took that 9pm slot!!), but there were plenty of times when we just walked on rides and we never waited more than 15 minutes to ride anything!!!!
4th...We've been twice in May and found that the weather and the crowds are both lovely.