To be honest, I thought the car felt like it was running rich during the medium throttle 2.5k-3.2k zone. Backing off the gas slightly smoothed it out. Plus, it was always far worse after the car had been sitting overnight, when it runs on a richer "cold" map anyway.
So I decided to use something that I thought might ignite a bit quicker than the 93 I'd been using. 91 is not available in my area.
A tank and a half of 89 later, and the stutter is almost gone. 3 tanks later, I'm noticing no power loss and a much diminished stutter. I really think the thing just runs pig rich on medium throttle applications in that 2.5k-3.2k zone.
So 89 has helped my stutter. FWIW, YMMV, etc.