The highest mileage airhead I have ever seen was an R100 that a friend of mine used as a despatch rider in London so fairly heavy going. He took it from 12,000 miles to 425,000 and changed the oil every 5,000 miles using the cheapest 20/50 he could buy. The top end was rebuilt every 100,000 miles and he never looked at the bottom end, the bike is still running. The moral seems to be don't waste your money on expensive oil in such a low-tech engine.
If it's in the Touratech catalogue then you don't need it
No man is an island, except for the Isle of Man