My guess is the owner's manual -- if you had a copy -- would recommend Yamalube 20W-40.
It's a V-Twin, but it's
water-cooled, correct? That's the key ... with a water cooled engine, the internal temperature ranges will be moderated.
Phoenix is hot in the summer, but not *that* much hotter than Tucson where I live. I've settled on running Rotella T 15W-40 dino oil in my 2007 Goldwing year round. See the series of UOAs
here.
The 5W-40 synthetic HDEOs are terrific oils as well. But in my opinion the value of those lies in
cold weather starts, as well as the
potential for extended changes. Synthetics are also better at very high internal heat, but a water cooled V-Twin, even in a Phoenix summer, isn't likely to stress that aspect of the oil.
So ...
- I don't think you'll need a 20W-50 oil ... unless your bike is air-cooled, but that would surprise me for a Yamaha.
- My opinion (based on experience) is that a conventional HDEO will work just fine