The 50 is going to give you substantially better protection at higher oil temps. If your oil never breaks 200 degrees, you probably won't utilize the additional protection. But if your engines never break 200, I'm guessing your temp readings are probably not right. Or you don't run more than part throttle.
Additives? Depends. They took alot out of oils so I see no reason why putting them back is bad. They took them out to reduce the emissions of metals into the environment. Replacing them isn't the most environmentally consientious thing you can do, but neither is owning a recreational toy that burns more gas in a weekend than the average American consumes driving to work in a year. Zinc (ZDDP) is a proven wear preventer. Molybdenum disulfide is an exceptional lubricant. Adding them back in certainly will reduce wear and friction.