Those are work horses why would you want to go at top speed? the tires are balloony and they really weren't designed for that style of riding, but I'd say around 60 mph.Well the 680 is probably around 40hp the rubicon is a 499cc probably around 25 to 30H.P.
I wonder this because I may switch my Rubicon to the rincon in a street legal version, a European tractor. these are machines that are registered on the white signs, and they are cheap You can use them on the highway, so speed is important so I can hold 55-57mph without destroying the machine entirely: P That's why I ask.
NOw that I can't answer for sure that may be a question to as your local dealer and get it in writing because if you get it and it fails while traveling down the highway at near wide open speeds your going to be hating things really bad.