I run 89 octane in my boat ('97 Merc 3.0 LX carbureted 4 banger) and find it runs much smoother. It actually runs even better on 91 octane, but 89 is a good compromise money wise. I've never had pinging issues with it, it just seems to run smoother. Maybe because of the slower burn?
2015 Silverado 3500HD SRW, CC, LB, 4X4, Duramax Z71
1997 Bayliner 1950 Capri Skinnydipper
2007 Springdale 291 RKL-GL
2 Each 2015 Can Am Outlander L 450 DPS