stilton,
Some very good questions and thoughts. If it was a good idea to fiddle with the trim settings, the test pilots at the factory would have made appropriate recommendations.
If you set the trim according to your Standard operating procedures and according to the Load sheet you will be legal and also probably live a long and happy life.
If you set your trim according to anything else, you may die, or worse still, live to regret your actions and the lives that you have lost as a result.