I run it because that's what Toyota recommends. There are stretches here
where it gets pretty damn hot during the summer and I still run it. You
should check out the website www.bobistheoilguy.com
The site really goes into detail about engine oil and differentiates myths and
facts. If you're really bored do a search of "Engine Oil Filter Study". A lot
of information on oil filters and oil filter ratings from someone who obviously
had a lot of time on their hands.
I live in Guam, it's between 85-93 degrees here year round. I run synthetic 5W-30 in my truck. It's what Toyota calls for. Just tipped over 60K miles on my '03 I've owned since new and have always used synthetic and always Toyota oil filters.