Octane plays a role in what compression ratio you can run without detonation. the higher the compression ratio you can run without detonation, the more efficient combustion is, and thus the better your fuel economy.
Now for us supercharged folks, you want to balance compression ratio with the effective ratio that is created at max boost. I wouldn't recommend running more than stock without a tune. I'm going to be running about 9:1 once my engine is put back together.
I noticed XR7 Dave has a group buy for rods and pistons and the pistons are a lower compression ratio. Maybe he's been learning something over the last few years of tuning that has him recommending that.