6'5, wow, didn't realize

If you have muscles to backup your height and some confidence in your abilities, I'd up the cc's to 500-600.
all depends also how deep are your pockets to cover cost and insurance as well... on plus side starting with a bigger bike will extend an ownership a bit as you won't get bored as soon as on a smaller bike... changing bikes often it's an expense on it's own where you lose a few bucks every time...
I know a guy in my gym who raced Downhill Mountain bikes and he started with KTM650sm and never had any problems, but he's one young aggressive cocky competitive bustard LOL
here is another reliable bike with comfort for longer hwy rides.. Honda CB500X
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