It gets super hot in AZ. 118 degrees is not uncommon during the summer. And it never gets below freezing where I live. The oil fill cap says 10w40. But if you look in the owners manual (I don't know where mine is at the moment) there is a temperature chart in there that shows which oils can be used in what temperature ranges, and it shows 20w50 covers the widest range of temperatures, far below anything I would think anyone would be riding in. I use it because it provides better protection for the engine. It has a higher film strength than lighter oils so it is less likely to break down and allow metal to metal contact. Also, because it is thicker, it stays on vertical surfaces longer than a thinner oil. I have put 190,000 miles on two Vulcan 750s, and never had a problem with it. I have owned more than 50 bikes total, and used it in every one of them. Again no problems. It's the only weight oil Harley Davidson recommends. You also need to be careful using lightweight oils because some of them are Energy Conserving, and can damage a wet clutch. While it does not specifically say so, the main reason all manufacturers recommend the lightest oil they think they can get away with is to save a mile or two per gallon in gas mileage, rather than make the engine last longer. You can thank the EPA for that.
As for the filters, K&N OIL filters may be fine. K&N air filters are crap. They are marketed as a "high flow" filter, and because they flow more air, they also flow more dirt. They also lean out the air/fuel mixture, which is already too lean on a stock engine from the factory. You can rejet to compensate for that, but if you are looking for more power, you won't get any noticeable power increase out of it. I prefer a reliable long lived engine. You can also blame the EPA for the too lean jetting.
As for Fram oil filters, I personally know of two car engines that were destroyed by them. The element came unglued from the can and plugged up the oil passages. Watch this video about oil filters. You'll see what I mean
There are plenty more videos like it.