What matters is the overall rolling diameter. If the new tire changes the overall diameter, it will affect the speedo and odometer.
OP, you understand how the aspect ratio works right? 35*265 mm width = 92.75 mm sidewall height. 30*285 mm width = 85.5 mm sidewall height. The sidewall is shorter so the overall diameter is smaller so the tire must spin faster.
2008 IB E92 M3| BBS | KW | Arkym | Platte Forme A.G. | Active Autowerke | K&N | Fabspeed | Dinan | Evolve-R