I don’t expect you’ll find the Rebel 250 to fit comfortably, but I could be wrong. Another 250cc cruiser to look into is the Kymco Venox. It is a 250 sized like a 500 or 750… Don’t worry if you’ve never heard the name Kymco before. Chances are one of the Hondas you’ve seen on the street was built in their plant.
There are people your size who do cram onto Ninja 250s, but you’ll have to sit on it for yourself.
As for dual sports, they are probably your best bet. There are a whole crop of 250s coming out this year (Yamaha, Kawisaki, and Honda I think). I’ve only seen a Super Sherpa (Kawasaki 250) in person at the rider’s course. It dwarfed the little 150cc bikes the rest of us were on. My sister (5’6″) was able to ride it comfortably, as was one of the instructors (over 6 foot, but not by a lot). I think it might handle your height. The power is certainly there you handle your weight around town. The bike has no problems pulling wheelies, as my sister found out! But I’m not sure how well it is geared for freeway speeds. If your goal is to spend time on the interstate, the DRZ400 is probably the best dual sport (short of moving up to a 650).
I’ve seen the Honda 230 dual sport at the dealership, It looked pretty tall. Without a rider on it, the seat was higher than a sport bike’s. Not sure how far away the foot pegs are, bu it is certainly worth looking at.
Any good dealership should be more than happy to let you sit on a display bike for as long as you want. Head out, spend 10 minutes on every bike that strikes your fancy. If you go when it is quiet you’ll probably have a bored salesman to chat with the whole time. And remember, just because you sit on their bikes doesn’t mean you have to buy from them.
I’d be really curious to hear your thoughts after you’ve “tried on” a couple of bikes.
Lastly, chances are you’ll fit a lot more bikes than you think. There are two guys in my office, each as large or larger than you. They’ve both been riding bikes for years. One guy is younger and drag races 80s sport bikes, the other is older and rides a Harley, but used to ride a 450cc UJM (Honda Nighthawk 450 I think) and loved it. The second guy loves small displacement bikes, go figure.