110 for me and we ride 80 MPH highways all the time here in Utah. I usually enter the freeway at 100 and back it down. 110 and I start getting nervous. On my 2010 Ultra classic, I would get the death scare wobble at that speed. I do not get any wobble on the Rushmore.
I am into speed, but not into tickets or jail. I had it up to 115, and it was solid. If it wasn't bone stock and I could get to 120 faster, I'd probably go for it.
The day after I had the bike Dyno tuned by GMR Performance, I took it out on a huge flat stretch of Texas Hwy just to see what she would do. Ran it up to 120, it was still pulling although you could start tell it wasn't going to pull much more than that. Solid as a rock and stable as can be. Happy to see it would do every bit of 120.
I had the dealership build me a 120r for my 14 SGS ive had it up to 200 kph -124 mph and that is fast enough for me. It's a little twitchy at that speed I mostly just like to cruise around 80 mph.
Fuel goes through these beasts at an alarming rate when over 80 and let's face it they are hardly performance machines are they so peak performance in the speed area isn't really an issue to most owners as they just want to roll.
Rolling along is what the HD are good at and one of the reasons I turned to Harley was to get away from the new for speed thing
I have been up to around 110, but after my foot flew off the floorboard/highway peg (heel toe combo) and touched the ground briefly at about 105 I don't go that fast anymore lol.