There is really no blanket statement as to which grade is oil is best for a particular motor. Generally one wants the least viscous oil which retains proper pressure in all situations. Hardly any two motors on here are exactly the same.
If you're not having any problems -- I see no reason to change. You can try different grades and see if it acts differently, but I wouldn't expect night and day...
In New Hampshire - 10W30 or 10W40 is probably fine for summer; you probably want to drop back to 5W30 if the car has to endure cold starts during the winter.