Digital Tuning Octane Question

Well, coincidenally I got an SCT tuner with a rear end package last May for my 2000GT. I tried everything in the book to get the 87 octane tunes to run my car, but they were terrible. Then I tried the 91 octane tune with prem gas and was shocked at how well it worked. I still use the 91 tune but have it modified for regular gas. For me I had no choice but to do it this way. I get good MPG too
My car is stock so YMMV, but if in difference do you mean power? I have not dyno'ed my car, but there is a very noticable difference in how long I can smoke the tires using premimum gas and the unmodified 91p tune.

the difference in the tunes should be mostly timing based. less total timing with the lower octane fuel to prevent spark knock and more timing with the premium fuel for more power

On a stock-ish N/A car, there is some difference, but it's really not much. I'd say maybe 8-10 rwhp and 12-15 rwtq. Enough that a keen SOTP meter could tell a difference, but not enough that you could really tell it if you didn't know about it. 25 degrees of temperature difference will make more difference in power.