What grade is everyone using? The owners manual says 87 but the serivce manual says 89. I know its not a huge difference but if running 89 will help the machine and run alittle better then ill start to use it.

[2015 Z Force 800 53/Trail EPS]

I find..as expected..that in hotter conditions where the intake air is hotter making the combustion temps a little higher, that a little more octane helps..but I don't go over 91. Then in the cooler temps like winter I drop back to 87 or 89. Does help cold starting. Keep in mind I am at 5400+ feet and the air is already much thinner then at sea level so cold air will be more dense at sea level meaning this like of thought may not have the same effect. Anyway..you are right in that the difference between 87 and 89 is minor but may be enough to feel in your situation...so try both, can't hurt.  

I run 91 and add about 4 oz of Seafoam to each fill-up. Each fill-up for me is about 4.5-5 gallons.  The machine spins like a top.  Not an ounce of trouble.  There is such a minimal amount of cost difference between the 89 and 91, that for me I'll stick with the 91. 

In general, you run the lowest octane which does not produce knock. These engines are designed for 87 octane. Lower octane can be used at higher elevation where the air is thinner and the compression lower, and higher octane can be used in hotter weather to prevent knocking with hotter running engines.

Running higher octane does not provide any performance benefits outside of knock prevention.

https://www.bellperformance.com/blog/bid/101182/What-Does-Octane-Do-In-Gasoline-Octane-Ratings

I know this post is older.

Doug is 100% on point.

I think people have misconceptions about fuel and octane.

Higher octane fuel isn't necessarily "better".

The octane ratings on fuel represent fuels ability, or lack there off, to detonate under pressure. This is why higher octane fuels are used in performance engines and should be used in vehicles with turbos.

The reason I use the highest octane I can find is that as fuel sits it loses its octane rating. It starts to go bad. Usually, it also doesn't have ethanol which collects water.

Basically I use it for storage since I don't ride all of the time. For people that are constantly riding it's not a big deal.