Every engine is a bit different - depending on mileage, how tight the engine is, how it's driven, aluminum heads vs. cast iron, what kind of shape the cooling system is in, they all vary a bit. You're not gonna hurt anything by experimenting a bit - try bumping it up a degree or two at a time, then drive it and see. If performance/mileage is helped and there's no detonation/pinging - then try a bit more. Back it off when you reach the point that performance isn't helped or pinging starts. And remember, it'll tolerate more advance in the cold air of February than it will in August in NC.
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