The most I've ever seen published of a dyno-tune/reflash is 1-3hp gain (which you would never feel). There's just not any top-end power to be had in these engines. They aren't designed for that anyway.
I think that 20-hp figure is probably down low, in the first 3 gears if they eliminate any kind of electronic throttle restriction.
Exactly. Ex and I bought a pair of 2013 S10's new from the dealer around Christmas 2015 when I joined this site. Hers was and is still stock aside from adding Givi luggage. I had Anthony reflash mine. Riding them back to back and doing side-by-side comparisons from a roll in several different gears the difference was obvious. My reflashed bike in touring mode was quicker to accelerate than her bike in sport mode. My bike in sport mode would just kill hers.
In sport mode and my traction control set to 2, the traction warning light will flash on briefly during a 6,800-7,000 rpm shift from 1-2 and 2-3 as the front wheel leaves the ground for just enough time to trigger the sensor. I'm fairly impressed by that since I weigh ~ 290 lbs geared up.
All anecdotal, yes. I did have my bike dyno tested and am trying to find the misplaced / mislabeled files this afternoon. If I can't locate them, I will call the shop where the testing was done and see if he can send me JPG's of the results.