Even if you drive like a grandma, you're running an aftermarket tune on an STi longblock. I don't know about your Bugeye, but mine says to only use premium right in the owner's manual, and I'm not even running a EJ257 like you. Running a 89 or lower octane on a 93 octane tune will induce increased knock and thus increased wear on your engine internals. Also, using a mid-grade fuel on a pro/shelf tune, you will get a lower MPG than with 93 octane, resulting in a lower amount of savings at the pump than you think you may be getting.
You have a great setup and clearly have invested a decent amount of time and money into it, it'd be a shame to see increased detonation screw up all the effort you've put into this.
Please, for the love of God, stay out of boost until you start running 93 octane.