I don't think mine's ever done better than that, but in 20 years I've never really checked it; I just make sure there's gas available every 100 miles if it's going that far.
Mine's 438", 2x4 inline original carbs, 10.8:1, 260* @ .050, .565/.547 lift, 4-speed, 4.10, 27.5" tire, 3800 lbs, see Attachment. I generally keep it around 3000-3500 RPM but I have a rule that every time out, it sees full throttle at some point.