I must admit I believed 91 was the recommended octane level for the ST1300. I think I got this from my ST's previous owner and I've run with it since 2016. I poured through the owners manual yesterday and there it was - 95 is recommended.
I think at 160,000km on 91 it might be too much of a shock for the old girl to be treated with 95 permanently, not to mention wallet shock!! I think I'll stick with 91 and throw in the occasional 95 or 98 "just in case" it does some good AND keep an eye out for ethanol stickered pumps.