Using high octane may or may not be helpful. Here in Canada, octane is boosted using MMT which is a manganese-based additive. Apparently, it is one of the best. Several of my friends with with vintage bikes (Velocette, Triumph, and Sunbeam) use no other additives in their fuel with no apparent valve recession. My Douglas has not been on the road long enough, or seen enough mileage to let me draw conclusions.
On the other hand, some other countries use different octane boosters which do nothing for valve recession. In that case, I'd use regular grade fuel with an aftermarket additive specifically designed to prevent recession. The cost of high test without valve seat protection is not justified, unless you need the extra octane to prevent pre-ignition.
