The Eco tune and the Stock tune (I have had them both) did not perform the same for me, caveats to this are, the Eco was loaded on my select-a-tune in my initial tune file, the Stock loaded on my select-a-tune on my dialed in tune file.
That may be a difference.
I have had smart-octane on both tune files, so that is no different... my mileage has improved since dial in, but mpg on 87-91-93 is no different per map.
I'd be willing to say there are no economic benefits to running higher octane whatsoever. This is my experience, only. I enjoy driving on 93 more, and it has some added utility in traffic situations, but that's about it.
I have heard claims of working out 1-2 mpg higher on 93 compared to 87. I'm not seeing it, and I am convinced I have a pretty good benchmark to weigh it against, of course be speculative, your mileage may vary.
Nonetheless I can do 38mpg fairly easily. If you keep your throttle slow and steady, your speed legal, and you avoid traffic jams, you should be able to also.