Does 95.8% silver tarnish as fast 92.5% silver?
If you look here: https://blog.centimegift.com/does-sterling-silver-tarnish/, it says that pure silver is very tarnish resistant. Sterling silver on the other hand being mixed with some Cu to enchance the metal's mechanical properties tarnishes as a result of the Cu in it. Therefore, considering that the amount of Cu in Britannia silver is smaller, it should tarnish more slowly than sterling silver. In practice i dont know if there will be a significant difference as the increse in silver purity is not that much.