Sadly, from my limited OS experience and resources it doesn't appear there are complete definitions for the 11 STi. With official releases stopped years ago the only ones added have been individually provided. The one I've used in RR to look at the 11 STi isn't part of the official definitions, and does not include all the tables necessary to implement per gear.
So, unless I'm wrong which is very possible, it looks like for some OS is the tool to use and for others ATR is.
However, the point of this thread isn't a how-to for implementing Per Gear Tuning, but more to bring awareness that the option exists and has proven, undeniable benefits. Those who have the desire to pursue such tuning will find a way. Obviously, one way is to get a pro to craft the tune... with one here, fahr_side, who already has years of experience at it. I'm sure there are others, but not all.
I've been so preoccupied getting my own tune off the ground and safe that my knowledge of who can and who cannot do what is poor. Some only have the possibility for per gear boost... perhaps the most important of the two because it provides for more power and more safety than any other option I'm aware of. Some have the option of both per gear boost and per gear timing... the later providing driving and performance enhancements.
In my opinion, anyone who values their motor and has gone past Stg1 should find a way to per gear boost tuning, at the least. Far too many of these engines fail just because of one high speed run. The records show that track days kill unprepared engines. Many people who believed, just because their tune was "safe" and worked fine day after day in normal use, was also safe at a track or a few high speed rolls in "Mexico" have lost motors.
Proper boost control that eliminates spikes in higher gears can be done other ways effectively. But, per gear provides not only that, it provides for even greater performance in the lower gears as well. No other method does that, to the best of my knowledge. With per gear you can truly have your cake and eat it too.