I think your height is more of a matter than your weight. I'm 6'0", "around" 200lbs, the bike has no problem carrying me, although it's a tad small. With the modded airbox, enhanced carb, and a D&D pipe, it'll pull 94mph on a good day(indicated).
Well to be honest, any extreme length of time on a bike is going to affect people differently. 6 hours on a bike is a bit of a long haul for me. I would break it up to in 3 hour blocks with an hour or two at a mid point for lunch and some rest. 500 miles you are looking at about 9 hours.
I'm 6'2" and I ride about an hour a day on the Blast with no issues. I also have the standard seat and not the low profile seat which could make a difference.
If you have never ridden this bike I wouldn't recommend the maiden voyage to be on a 500 mile road trip.