I am about to change tires (I think I am going to go with the ME880.) For the rear I am going to fit a 140/90. I am not sure about the front. I know stock size is an 80/90. Is there any benefit in upgrading to a 90/90? Is handling worse or better? Any opinions/ ideas? Thanks.

Best stick with stock sizes, there is usually no advantage to upgrading (apart from a style issue) and sometimes it can upset the geometry of the bike, making it "tip" into corners more.

A lot better handling with the 90/90 21 size.........

(even better if you slip the fork tubes up the triple tree a little)