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Yes. The spring will provide a base level of boost control. A boost controller can then allow you to run higher boost to a level of your choice. Although general rule is that you can safely run 2X the boost of the spring, so on a 5lb spring if you wanted to run 15psi--->while it may work, you'd be better off upgarding to say an 8-10lb spring.
What's wrong with that? It means running 93 is just an added measure against detonation. I wouldn't expect much (if any) power gain from running higher octane fuel, it's mainly a safety measure.