Rotella synthetic is what I would use in my tractor, if I didn't already run Delvac 1 synthetic in it.
I've used the Rotella T synthetic 5W-40 from my first change at 50 hours on my CK30hst. I took the advice from DK35Vince. We have similar weather. The tractor starts easy on those 10" days and runs fine in the Summer heat.
Deere Plus-50 II Premium Engine Oil suggest up to 500hrs drain intervals. it takes me a while to get 500hrs on a machine. I plan following the manual for my Kioti and on my other tractors I usally change at 100hrs. Here is a good site for info on tractor oils. CountryMark