Corrosion is strictly experimental. Previsions don't work. Unfortunately, I never used such a steel. Silicon is often claimed to improve the corrosion behaviour of already good steel, but alone Si in Fe won't make stainless steel.
Would you tell what your 6.5% Si steel is? I know mechanical steel up to 1.8% only (for springs) and transformer steel with 3% Si. Is it brittle? Can it be forged? How difficult is the heat treatment? What advantages? Is it transformer steel from NKK?
I fear this steel is uncommon, so data must be scarce. Ask the manufacturer, or make your experiments.
In my experience, 3% Si transformer steel is far from brilliant. Water corrodes it quickly.