I've read a few threads that talk about putting an RT sway bar on the F3S and that it makes a difference. .
I haven't done it to our F3 but I think I know the answer. I don't think it will do anything materially worthwhile...
Our 2009 RS is tricked out with all sorts of performance options including sway bar and Elka front shocks. I can easily lift the inside front wheel around 15 to 30mph corners whenever I want to, and would normally do that at least twice a short ride, just for the sheer fun and exhilaration of it. ;-)
It came with an orange after-market sway bar, and I was told at the Spyderfest in Durango in 2014 that it was junk, so I had an RT bar fitted. The big thing we noticed with the RS was that it leaned a lot during cornering, so much so that it felt unnerving. There was no real improvement with the RT bar.
We also had the upper shock relocation bracket fitted because that would make it more like the improved '13+ models. It had no real effect either. I now know why.
We rode 2014 models at Durango and it was very obvious that even the stock RT would corner much faster and flatter than the RS, so we spent no more money trying to improve it and bought a very low mileage F3-S in February - stock everything except for that beautifully throaty Akrapovic. Yes, even though the rear suspension was on the bump stop two-up, and even though it would bottom out with one rider aboard, it was a night and day improvement over the RS in handling.
Try as I might I have not succeeded in lifting an inside front wheel on the F3.
One-up or two-up, entering freeway on ramps from a stop, I can apply so much power that it is noticeable, even to my wife on the back, that it is starting to slide, but is kept under control by the stability control system. I would never dare try that on the RS because it simply did not feel stable, especially with a passenger. When I ride pillion, which is frequently, I have no fears about how hard my wife drives; in fact, I keep urging her to corner faster, which she does. The F3 leans out somewhat, but not like the RS, and never is fear-inducing.
Why? The radical relocation of the A-arm suspension pivot points in 2013 or 2014 is what made all the difference.
Does anyone need a different sway bar on an F3? Probably not. A different rear shock, or different springing, though, is essential if you have more than 100lbs on the rider's seat.