My tune went into a V6 truck so your experience may vary slightly, but the principles should be the same. I'll do my best to answer your questions.
1. Benefits of firmer shifting... If your transmission is built to handle it, and you've got the rear tires to put the traction down, it can mean faster track times. Other than that, not many benefits IMO. Especially in a daily driver.
2. Torque "percentage"... What you're referring to here is called "torque management," and you have the option to reduce it, not add it in. This is one ingredient to faster shifts, but it goes back to what I said earlier about your trans being built for that sort of thing. When I first got my tune, I had Black Bear Performance remove 100% of the factory torque management. A couple weeks later, my stock 4L60E grenaded during a WOT shift into second. Call it what you will, but I'd say that'd be one hell of a coincidence. I had the trans rebuilt with lots of internal upgrades, and after that the shifts were too hard for my liking. I sent my tuned PCM back to them and had the TM returned to factory and the truck still breaks traction shifting into second every time now. Like
@Jrgunn5150 said, if you really want quicker shifts, trans parts are the way to go. I'm now a firm believer that the factory torque management is there for a reason.
3. Power of 89 vs 87 octane... Justin at Black Bear told me that these trucks can see very mild gains by tuning for 89, so I did it. When I sent it back to have them put the TM back in I went ahead and had them switch it back to 87 though, and to be honest I can't tell a difference at all between them. Not worth the extra fuel costs IMO.
4. MPG gains... Not going to happen in my experience. Economy will stay about the same.
5. Worth the money? Absolutely. Most noticeable thing I've done to the truck by far. Made it much more responsive and fun to drive.