I have an '85 Rebel 250. I'm 5' 10.5", and weighed just over 200 lbs when I was still riding it. It would DOG on hills in 5th, and I'd frequently have to downshift as far as 3rd to get it up them. I also have a windshield, so if I have any headwind at all, it'd slow me down as well.
When I first got mine, the vibration was so bad @ speed that my hands would be numb when I got to work (17 mile commute). How I got around the vibration @ highway speeds was to move to aftermarket sprockets - 15/30 for me. I went as low as 27 on the back, but that was an aluminum one which didn't last long. 30 is the lowest tooth count I could find a steel one in.
Just know that you'll have to downshift a lot, especially if you go with different sprockets.
Peace, Blane The friendship of the Lord is for those who fear him, and he makes known to them his covenant. - Psalm 25:14 Whether you think you can, or you think you canít, youíre right Ė Henry Ford Life is ten percent what happens to you and ninety percent how you respond to it. - Lou Holtz